Hey, I don't think Opterons are "half-decent" as you say. They're really nice, in my opinion. I've used Pentium 4's before with 3 - 3.4 GHz clock speeds, and they were about as fast as my 2.2 GHz Opteron while running single applications. There was a noticeable gaming difference (graphics cards were similar) though I do acknowledge that multitasking with a Pentium 4 is somewhat smoother.
And, asking that question, with no real "guidelines" is going to get you a lot of answers, as shown here. I agree with them; AMD's are better in some respects, and Pentium 4's are better in some respects. I do believe they're about right, though, a 3200+ (which is 2 GHz, if I'm not mistaken) is probably around a 3 GHz Pentium 4 (this is approximate, just from my experience overall).
And, asking that question, with no real "guidelines" is going to get you a lot of answers, as shown here. I agree with them; AMD's are better in some respects, and Pentium 4's are better in some respects. I do believe they're about right, though, a 3200+ (which is 2 GHz, if I'm not mistaken) is probably around a 3 GHz Pentium 4 (this is approximate, just from my experience overall).