Instructions per clock
I sat down and figured out the Instructions Per Clock of a set of x86 architectures. You can use it to compare the raw single threaded performance of any architectures.
e.g. a 2.5GHz Core 2 ia about the same as a 3GHz Athlon 64 x2
Pentium 1 1.1 Pentium MMX 1.2 Pentium 3 1.9 Pentium 4 (Wil) 1.5 Pentium 4 (Nor) 1.6 Pentium 4 (Pre) 1.8 Pentium 4 (Gal) 1.9 Pentium D 2 Pentium M 2.5 Core 2 3 K6 II 1.1 K6 III 1.3 Athlon B 1.9 Athlon C 1.9 Athlon XP 2 Athlon 64 2.3 Athlon 64 X2 2.5 Via C3 0.85 Via C7 0.9