I'm not taking sides here, just voicing some oppinions both ways. I love the Z32. I don't own one, but have test driven a few as I plan to buy one in the future. My father has a fairly stock 1988 C4 corvette. I've ridden with him many times in his vette (and he's no slouch, he has some scca experience), and driven the car myself a few times. I will say the vette is pretty fast in a straight line (definitely has a fatter low end than the Z32) and handles extremely well on a tight, winding road (better than my 240z, even with 1000 extra pounds).
However, the build quality is crap, and the car shares most of its parts with my old 85 Camaro; engine, trans, door handles, switches, knobs, etc, etc. (that's how Chevy kept the price down). Whereas the Z32 seems more like an "upmarket" car in terms of build quality (and its original price lol). When the C4 first came out, all the magazines praised it as being the "futuristic supercar that will change the industry", and all that crap. Then they said the same thing when the new Z32 came out 5 years later, so you have to take it all with a grain of salt.
Now, when you compare the Z32 to the C4, stock for stock, you have to consider the years. Since TPI C4's were almost identicle from 87-91, we'll call that "early" and since LT1 C4's were almost identicle from 92-95 (barring ZR1's and GrandSport's), we'll call that "late". Z32's were pretty much identicle their entire production run here in America, so you can use pretty much any year to compare them to the vette. Autocrossing trophies aside, generally comparing the "early" era C4 to the Z32, its fairly even in terms of performance (stock). The accelleration is pretty much even (both cars regularly record mid to low 14's in the quarter mile stock), and when new, both cars were praised by the magazines for their handling (with at least one account crowning the Z champ). The "late" C4's actually are a bit faster than the "early" ones (makes sense when the LT1 is rated at ~300hp vs. ~245hp for the TPI, even though we all know Chevy underrated them). I've driven a 94 vette and can say it was faster off the line than my dad's 88 (also had a nicer interior).
Overall, I would say that just becuase the magazines say one car is faster, doesn't make it so, and just becuase one car is more dominant in autox, that doesn't make it better either. I don't know much about the rules in Solo II, regarding what you are allowed to modify on the car, but maybe something in the rules has influenced the C4 dominance? I personally think the Z32 is slightly better than an early C4 overall, but slightly inferior to the late C4 overall.
Now here's the thing: the Z had much narrower tires stock than the C4 (f/r: 225/245 vs 275/275), and anyone with racing experience knows that tires are the single most important factor in a car's performance, especially when it comes to handling. Of course I'm only speculating at this point, but I believe a Z32 will outperform any stock C4 as long as you run similarly wide tires and maybe install the "HICAS eliminator kit" and/or stiff bushings (to fix the "handling feel" issues BRAAP mentioned). That's what I plan to do when I scrape up enough cash to buy one anyhow! lol
Sorry for the long post, I just thought this was an interesting thread! And good write ups from the owners of these cars too.