I've owned three '65 Corvairs, two 90 horse automatic Monza models, and a quad-carb 140 hp Corsa. I've driven all of them, a lot.
The two 90 horse automatics were like electric cars, amazingly smooth, effortless, and reliable even in constant city driving. Their fully-independent rear suspensions gave excellent ride and control over even the worst of rough roads. The first one I bought had bent push-rods on one bank, I have no idea why. I replaced them myself, and never had this problem again, on any of these cars.
The 140-horse Corsa had a 4-speed manual transmission. I replaced the tires with FR -series sizes on the front and GR-series sizes on the rear, mounted on 5" and 6" wide 14" Chevy wheels, which bolted right on, then installed HD shocks all around. The handling became amazing. Porsche switched to the late Corvair rear suspension in 1991, in case you still have any doubts. I didn't.
Greedy fool that I am, I pulled off the four carbs and installed an aftermarket cross-ram maifold and an WCFB Carter 4-bbl; it kicked the torque peak up to around 4000 RPM, and the torque went WAY up. In second gear, it could out-accellerate our 1969 GTO 4-speed in second gear. My four sons, teen-agers then, and I subjected this lovely little hot rod to what probably constituted new dimensions of abuse for several years; one of them told me, years later, that he'd had it up above 130 mph indicated, and I don't doubt it at all. The tranny finally broke under the strain. For those who'd like to repeat this experiment, the '66 and up 4-speeds used the internals of the Corvette 4-speed, and they bolt right in. For that matter, the '66 140-horse 4-speed Corsas wouldn't have that problem.
I rebuilt this engine myself, and was amazed at its quality. Every Corvair boasts forged-steel connecting rods and crank, and a gear-driven cam; They're extremely reliable, and keep sharp tune as a consequence.
Best handling cars I've owned, very reliable, and excellent both in small and large design matters. Superb panel fit and paint. After 50 years (!) the doors still fit perfectly and body rust is minimal. The full instrumentation on the 140-horse Corsa was among the best I've ever seen, nearly as good as our '62 Studebaker Hawk, which is the best I've seen in 30 years working as a mechanic and automotive journalist.
The high performance versions were genuinely fast.