Long, but relative informative post incoming:
So, i took some time to share some cars with impressive specs that should be able to compete with the more commonly used top cars of GT5.
I haven't bothered with the cars that have already been mentioned here, but of these, I can say that i'd recommend the Caldina GT, Odyssey, C30, M3 GTR and the Kusabi. These don't only go fast for their class, but also handle superbly when tuned correct.
Now on to the cars that I have chosen to highligt. I've chosen to focus on the cars that produce the most BHP, which I guess is what the OP was asking for. It's also easier for me to spot these in the garage. Note that these aren't the only top sleepers that exist, just many of the ones that Im aware of:
Cars, that go faster than you would think: (sleepers: tuned and supposedly driveable ones. Tunes can be obtained from here:
https://www.gtplanet.net/forum/showthread.php?t=198751)
Jensen Interceptor MKIII 74': beautiful oldtimer with 700+ BHP. Very fast in a straigth line, a handful to control in corners. I'd recommend that you tune this car to make the most of it.
GTO 5.7 coupe 04': I haven't tried the available tunes for it as of yet, but I have it modded in my garage, and it sparks more than 800 BHP. I would suppose it's a quick car. Looks kind of normal too, adding to the sleeper effect.
Stagea 260 rs Autechversion 98': One of my favourite sleepers. Almost 600 BHP, and 4WD drive. Fast of the line, like, really fast, and with RVR's tune I've managed a 6.55 lap at the ring. Untuned, it likes to do insanely easy to hold 4wd drifts. What makes it even more satisfying is that it is what I would describe as a sporty mix of an SUV and small peoplecarrier, or MPV.
Eclipse gt 06': A FF car with 520 BHP is pretty unusual, which is why I think it deserves a mention. Since the tune that's available is quite new, I haven't tried it, but I think I'll givet it a go some time.
Holden Monaro CV8 04': Tried Skunkys tune, and had a lot of fun with it. Can't remember the characteristics of the car, but it's powerful and very quick with almost 750 BHP. Looks similar to the GTO.
Tom's X540 Chaser: Haven't tuned my own, but as the others, this car is powerful and should be checked out if you like sleepers. Mine's got 667 BHP, weighs under 1250 kg's and looks like a pretty standard, though a bit sporty, family car.
Lotus Carlton 90': Looks like your standard family sedan with an immense and not exactly pretty looking front bumper. However, it produces around 700 BHP and while I find that it doesn't handle well at all when untuned, some tunes might have changed this. Pretty common to see online for a sleeper, but that doesn't make it worse.
Supra RZ 97': Not sure if it classifies as a sleeper, but it's proper quick and there's a load of tunes available for it. 720 BHP makes it easy to understand why this is used as a tuner irl, and vice-versa.
Caddilac Cien Concept 02': As the supra this one is not really a sleeper, but it's not very common as well. 950+ BHP but hard to handle, so use a tune.
Holden Commodore SS 04': Haven't really driven this for a long time, but the specs are very similar to the Monaro. Can't say much more about this one myself unfortunately, but you might want to try it out.
Audi Pikes Peak Quattro 03': 730+ BHP, and looks like it would do fairly well at offroad driving. Again, the car wasn't desigened for all those BHP, so the handling is poor. Luckily, RVR released a tune for it, so the handling should have been sorted out by these guys.
*EDIT*Lotus Evora 09': Forgot to mention this, but it's amazing when tuned correct. I've used vengence's tune and it's amazing, one of the best I've tried yet. And I guess it also classifies as a sleeper, since it's kind of an underdog. Just think it deserves to be listed here as well. You have to try this one.
Cars, that has potential to go faster than you would think: (tuned cars, that have enough power, but are a challenge to drive; sadly, there are no tunes of the cars on gtp yet. If you feel like toying around with these and end up with a good result, please, do share them one way or another)
FX45 concept 02': 4WD, 600+ BHP, weighs 1250 kg. Surprisingly, no tune for this car, even though it needs one badly. Also, it looks good imo.
Aston Martin V8 Vantage ‘99: Why is there no tune for the only 900+ BHP Aston Martin here on gtp? It should be a no brainer, especially since it handles so awful in modded, but untuned conditions. Heavy, but powerful car, that would really benefit from a tune.
And last, but perhaps not least, a few cars that I haven't modded yet, but suspect to be rather fast when modded; (Both untuned and tuned cars)
Jaguar S-Type R 02': Well, I don't know If it will perform well, but my untouched model in my garage should have around 400 BHP after the oil change. The big engine, 4200 cc, should make it a powerful beast when tuned, and it looks like a pretty business type jag. I know i'll be modding this myself sooner rather than later. Unfortunately, no tunes exist for it though, so you migh find that it handles poorly.
Nuvolari Quattro 03': I haven't modded mine, since I only have one so far, and keeping that one stock. Think i'll dupe one as soon as possible though, since it has some amazing specs when modded. According to one of the tunes available, it has more than 850 BHP when tuned, and it's rather light for a car with that much power. Also, it's 4WD, and looks absolutely stunning imo.
Cizeta V16T 94': Not really a sleeper, but it seems to be quite quick and isn't commonly used online. 800+BHP. Look up the fully modded tune if you want to.
Jaguar XFR 10': Pretty much the same deal as with the Nuvolari; I've only got one, and I'm keeping it stock until I've duped it. It seems that the car can get modded to a high number of BHPs. However, there's only one tune for this car available on GTP, and it's for a stock version, so not certain about the car's performance when tuned.
And that's pretty much it. I'm sure that there's a fair number of muscle cars that will perform likewise when modded, but I'm not really into those, so I kept them off the list.
Hope you found the list useful.
