Your AROS experience is unusual.
Never encountered that, and I've been using it daily for about 10 years.
Problem must lay elsewhere. Its definitely not AROS itself.
If I can run dark places (massively enhanced quake port requiring pixel shaders and gl2+) at 1920x1200x32bit at over 400fps I suspect it could handle SpecBas
As for os3.x, along with my Amiga I also have an Amithlon box which I use fairly often. Running on a 4ghz c2d it gives me raw 68k speed somewhere around the ballpark of a 2ghz g4 running native code.
As such I tend to use it for things not really suited to a real Amiga, but it is fun using software that's normally not an option on OS3.x.