So I finally managed to unlock the 3 Forza Edition cars locked behind the Car Mastery system. After spending a good amount of time with each and tuning each car, here are some of my thoughts, in order of favorites:
NISMO GTR LM FE: Hooollly cow this thing is fun. It's the base GTR LM but converted to AWD, completely maxxed out, and comes with an Event Influence bonus. The Grip on this thing is insane, and it's pretty much a go-kart at all times. After tuning mine up, there are very few corners that it won't take flat out. It comes with Forza Aero, but the already high mechanical grip meant that I could at least remove the fugly rear wing without a noticeable drop in performance. Compared to the Zonda R & Vulcan and their respective FEs, the GTR is not as fast overall, but it is a lot more controllable, and has the lowest overall cost of all the high-end FE cars, both time- and credits-wise.
Reventon FE: Surprisingly, this one is kinda lackluster. The only really noteworthy thing about the Reventon is that it's engine has been swapped out for the Racing V12 (aka the F50 GT engine). It comes with a Credits boost, which should make grinding for money a bit easier. Otherwise, there's not really anything special performance-wise going on, it's neither good or bad. Some suspension tuning makes it a perfectly fine racing car, but S900 is otherwise the perfect spot for it. On the flipside, it looks badass, as it has a really cool carbon-fibre paintjob and the wheels match the yellow/black FE license plate.
I also have 2 of these, due to getting a Miura in a wheelspin, but I can't sell the 2nd one because there's a limit on how many cars you can auction per day.
Sagaris FE: It has the V12 From the Cebrera Speed 12 and pushes 1100 HP to the rear wheels. Needless to say, 1st gear is pretty much useless in it once you get moving. If you want it to be moderately useful as a racing car, you'll probably A) Give it Forza Aero, B) Convert to AWD, or C) Both. No matter what, making this a decent track car means moving it to X-Class. I also
highly recommend stretching out the gears. Mine is basically a very long 5 speed, but the car makes so much power that having very long gears actually helps more than it hurts. That being said, with good suspension tuning and careful throttle control, it's a real stormer. I was able to get two sub-48 second laps on Bamburgh Coast Circuit, while staying RWD. Meanwhile, both my Vulcan & Zonda R FEs could only do mid-48 second laps. Even still, given how many skill points it takes to unlock this thing, it's almost not worth it, because in almost any other situation, the car is near-useless due to its power.