There really is no comparision with dual-cores. Wether it be an X2 or a Pentium D, you really won't notice any difference at all. Sure, an X2 may finish a task 3 seconds faster, but when you're processing it and finishing it roughly 30 to 45 seconds faster then a single-core, does 3 seconds REALLY make that much of a difference?
Come on people...Let's use common sense and judgement here. An AMD X2 may be faster, but in reality, you won't notice the difference unless you had a Pentium D running right along side it. Are people really going to sit there with a stop-watch and say, "See! I beat you! I'm 5 seconds faster!" Seriously folks, when it comes to cost, the Pentium D is a better choice for those on a budget, the X2 is nice, don't get me wrong, but it's nearly $100 more, with that much extra money you could get an extra 512MB of RAM. And then that's when the performance aspect really shines...A Dual-Core CPU with 512MB more RAM, or a Dual-Core with 512MB of RAM less? Which in the long run will win?