Especially these days. Current-gen x86 architecture has all kinds of insane optimizations and special instruction sets that the Pentium I never had (e.g. SSE). You really do need a higher-level compiler at your back to make the most of it these days. And even then, there are cases where you have to resort to inline ASM or processor-specific intrinsics to optimize to the level that Roller Coaster Tycoon is/was. (original system specs)

Yep but not if you write sloppy C code. Gotta keep those nuts and bolts tight!