This was always the issue with the Amiga and CPU upgrades due to the whole Amiga custom chips.
Crap scrolling and slow fighters on Street Fighter 2 on MS DOS playing on your 386? Get a 486DX and everything magically improves to arcade levels of quality. On Amiga you can load up US Gold's SF2 conversion on an 060 you spent £750 on and it will still be mildly better than a £299 ST.
I also started a thread about a year ago about why the hell was Amiga basically given such bad coin-op conversions. The Amiga is capable of something close to Sonic if you look at Kid Chaos, ditto Outrun and Lotus II, Shadow Fighters and SF2 etc etc.
It is quite sad looking back just how bad many conversions were and the best software was mostly original arcade games not arcade conversions. Luckily there were 1000s of games and there are plenty that will make your jaw drop.
Add to that there were plenty of more intellectual games like the Magnetic Scrolls adventures which were just pure class and superior to the PC versions 
If it was out on OCS/ECS then PC version would be EGA = PANTS! :roflmao:
It's not really the upgraded processor nor the custom chips that were at fault it was more down to sloppy/ lazy conversions by the software houses in order to release the latest titles on the Amiga back in its heyday in my honest opinion...
Way back at the start of it all (the A1000 era) it was more down to the programmers not yet understanding just what the Amiga was capable of or having yet discovered the secrets of the machine. Take some of the very first games for the Amiga "The Feary Tale Adventure", one of the best games ever written for the Amiga IMO, for it's time brilliant gfx/ music & concept but let down by some badly written scrolling routines and a simple case of the programmer not yet having discovered quite how to programme the Amiga to it's best yet...
While I was never a big fan of the beat-em-up style games, to me it was a simple case of checking them out first before actually buying the things, if it was badly coded and played like a dog the answer was simple, I wouldn't buy it just because the gfx looked good...
I could never see the the point in paying around £25 for a game that had been badly converted/ported or rushed out by the software houses in order to grab their share of the market. Games like the Lotus Trilogy , Pinball Dreams/ Fantasies etc... are prime examples of just what could be achieved on the Amiga by good programmers and those were indeed worth every penny paid for them...
