I suspected that, as base
I suspected that, as base cars, the Mazda may be marginally quicker than the Fiat.
However, it really doesn't matter. Why?
Well, because the Fiat has a turbocharged engine. One that is designed to put out much , MUCH more power, very easily. The Mazda does not.
See, with a turbo engine, producing MUCH more power takes about 3 minutes. You just buy an aftermarket tuning program (which usually produces more power primarily by producing more boost from the turbo), plug it in, and away you go. And if you want more power, bolt on a cold air induction,which might take another 5 minutes.
How much more power?
Well, my experience with the Abarth engine is that about 50 more horsepower can be reliably bolted on/plugged in in about 10 minutes.
That simply is NOT possible on the Mazda, because no program is going to give you more than 5 hp. No CAI is going to give you more than about 7 or 8 hp.
In other words, in the real world, the Mazda will be much, MUCH slower to anyone who really cares.
A Fiat 124 Abarth with, say, 220hp would devastate a Mazda or a Honda S2000, or a lot of other cars.
Wait a month, then talk to Eurocompulsion or one of several other companies doing Fiat aftermarket stuff. It'll be a lot of fun.