Yup, no such test exists yet. And really, it would have to be the same car. Too many variables otherwise, chassis stiffening, ride height, 40+ years of wear and tear on the chassis (rust, damage, etc). Even with different cars that were the same make and model you could still have more than enough differences beyond the suspension to make an across the board comparison problematic.
There is this article though, for the muscle car of the year shootout hot rod did in 2013. Wracks71's fully RMS equipped Duster and the Hotchkis Taxi both took part, and you can see who had the fastest time. Hint, it was the 1970 4 door Satellite with torsion bars and leaf springs. Now, it's not a true comparison. Different drivers, different cars, different tires, just too many variables for it to be a valid comparison of suspensions. The only thing you can take out of it is that going fully coilover may not make you faster than a torsion bar/leaf spring car. Really though, you can't get past that. Even if you showed that one suspension system was better in certain performance situations it would be no guarantee that any one person/car would be faster with the "better" suspension.
2013 Muscle Car of the Year - Popular Hot Rodding Magazine
Yeah the 328's aren't a slouch. And a second per lap with the same driver and same tires is significant. Not the end-all-be-all though of course. Especially with autoX and road race cars it really depends on the track. You can set up an autoX course where miata's will kill corvette's all day long and not have it even be close, and then turn around and put them on a different course and have the 'vette's make the miata's look silly. Which comes right back to all suspension design and set up is a compromise.
Converting to the RMS just for the steering rack is a pretty big expense. You don't have to buy rebuilt boxes anymore. You can go Borgeson and ditch the original design power box all together. Heck I run a brand new Flaming River manual box, and that was a big improvement.
Also true. Of course, the problem with comparing roll centers, camber curves, roll axis, CG etc on a torsion bar car is that you can change most of those just by lowering the car an inch with the torsion bar adjusters. Or by running FMJ instead of A-body spindles, although Mopar Muscle did that comparison for roll center, bump steer and camber curves. Swapping Disc-Brake Spindles - Mopar Muscle Magazine. But yeah, at that level of analysis you'd find differences even from one torsion bar suspended car to another, especially if you start throwing adjustable UCA's and strut rods around.