I see no point in making speedy CPUs for Amiga. C'mon even if they made it possible, what would you do with it, play Lotus "on crack"?
Is it worth the money just to run Quake with impressive frame rate ? I seriously doubt it would substitute your currently used PC/Mac. Modern day computing power seems to be useless when you don't have proper software. That's why my old BeOS machine remains idle these days, as I cant watch YouTube videos on that (not counting some VLC methods which did the trick in 2007). To me Amiga is a great retrogaming machine with priceless sentimental value, therefore any attempt to make it "up to date" in terms of contemporary cpu power looks a bit over the top.