How do you compare the drive between the two ?!
The BRZ is sublime "in the canyons". Once you get it in a place where you can keep the engine on the boil (i.e. above 5000 all the time!) the deficiencies in the engine's delivery go away (it has a crappy mid-range which is the Abarth's strength). Also, the best mod you can make to a BRZ is decent rubber, and ours in on Dunlop SP Sport Maxx RT (they are like Play-Doh) on lightweight STi rims with lowered STi springs...and it makes quite a difference. Most comparison tests you see between the MX5 and 86/BRZ are done with the 86/BRZ wearing it's OEM "low grip" Michelin Primacy boots. Put an MX5 and the 86/BRZ on the same quality rubber and I'm not sure they'd be as close.
Haven't had an opportunity to punt the Abarth quickly yet, and as I'm going to be overseas for the next 3 weeks, it's going to be a while until I get the time. Initial impressions are that the BRZ is a little bit pointier and has the (slightly) better steering. The seats and driving position are a bit better on the BRZ too...although ticking the Recaro box on the Abarth would fix the seats (not that the standard ones are that bad). I really wish the Abarth's steering wheel was adjustable for reach though because, in the BRZ, I like to sit a bit closer to the wheel. But, apart from that, initial impressions are that the Abarth is on another level for equipment and finish...and I expect the driving experience to be really good. Better impressions to follow...