My experience with performance upgrades is that you have to look at the package as a whole. That is, bumping an 88 to 95 will increase your displacement and more than likely add a few ponies, but the issue of whether that turns into neck snapping performance is another matter. A lot of times, just taking a stock motor and letting it breathe better (head work , cams and exhaust) can do more for performance than extra cubes. I recall a guy I knew as a teen who campaigned a '55 Chevy 150 at the local drag strip. He was as competitive, or sometimes even more competitive, as guys running big block motors. His power plant? A little 265 small block. But this baby had everything done to it that was legal in his class (D/Gas). The heads were put on a flow bench, the entire rotating assembly was balanced, the cam was specifically ground for his motor, I mean it just went on and on. The question, IMO, becomes just how much do you want to spend, and just how much horse power do you really need?