Went to try out a 124 Abarth (6spd with brembos) this weekend. I deliberately drove my Boxster ('99 2.5L 5 Spd) to the dealership so the Porsche's feel would be fresh in my head for comparison. I've also driven an ND.
The 124, as I sort of anticipated, feels very similar to the ND. It didn't feel quite as "roll-y" as the Mazda, but there is still an annoying amount of body movement in the chassis. Everything about the 124 is very light. The clutch, shifter, and steering all require far less effort than my Boxster, which makes the car a little easier to drive, and also easier to drive hard, which I did.
The engine was a bit of a let down. I was expecting it to have a little more character. I was hoping for a bigger payoff when the boost came on, a little bit more drama. The exhaust sounds kind of cool. Even though my Boxster is the slowest manual boxster ever, it still feels a fair bit quicker than a 124 Abarth, especially acceleration from speed. The Boxster also has a smoother and far better sounding engine (lovely induction noise right behind your head) and is more enjoyable to bring to the upper rpms.
As mentioned before, the 124 feels much easier to drive fast, and the limits are much more accessible/less scary than the Boxster, which itself is pretty forgiving, especially for a mid-engine car. I was getting rotation from the rear of the Abarth pretty easily, and not at scary speeds. The Boxster would feel much more planted at the same speeds/corners.
The most stark difference between the 2 was the steering. The 124 has almost zero steering feel. This actually surprised me. Jumping back into the Boxster after trying out the 124 I immediately realized how alive the steering wheel of the Porsche feels. The 124 has a little bit sharper turn-in, but I can't help but feel that's due to much higher levels of steering assist (combined with much thinner sidewall profile tires). However, the 124 wallows quite noticeably in transitions, whereas the Boxster stays level and planted.
The manual top on the 124 is a joy. I really dislike the slow and mechanically-complicated power top on my Porsche. As a result, I don't put the top down as often as I would like. The 124 takes like 5 seconds and you feel it will never go wrong. The interior is also pretty awesome but I did have a little bit of trouble reading the tachometer, as there isn't much contrast between the numbers and the red face, especially when wearing sunglasses. It feels like a quality thing.
At the end of the day it's not really a fair comparison, as the Boxster was a $50k car new (not adjusted for inflation!) and the Abarth is a raced-up $24k MX-5. I think most of my complaints about the Abarth can easily be fixed (lack of power, and poor body control) with aftermarket mods (ECU tune + better dampers/rollbars) for not much money. However, I'm not sure the lack of steering feel could really be remedied. It's still the best new car I can think of. I liked it better than the GT86, ND, or 370z.
My Boxster handles better, feels faster and feels more serious/mature. The 124 is easier to drive hard and produces cheap thrills. In the end, the 124 (and the MX-5) feels a bit like a toy. It's still compelling though. I need to drive a GT86 back to back with my Porsche....
Side note: 986 Boxsters are just about the best value sports car right now.