I think your best bet is to get out an drive a couple more zeds - see if this 'box you experienced was just a bit cold and notchy or was it on the way out. If you were out for twenty minutes or more and it was still 'notchy' then its probably the latter. If it was less than that I really don't think you can make the call and defo get the tyres up to 35!
Also decide if you want a track car or something you can enjoy thoroughly on the open road and with a modicum of tweaking also enjoy just as much on track. As far as 'inertia' goes...well obviously the zed is no Elise through the twisties...but IMHO you'll have just as much fun finding it's limits
Though am still not clear why you would attempt to make comparisons with an M3, an M5 and an MX-5