They're the same speed. Tested with 3 PCs.

1) My PC:
Intel Core2 Duo 2.53 GHz.
NVIDIA GeForce 8600 GT.
2 GB RAM.
Windows Vista Ultimate SP2.

2) :
Intel Core2 Duo 2.40 GHz.
NVIDIA GeForce 7200 GS.
2 GB RAM
Windows Vista Home Premium.

3) :
Intel Centrino 1.50 GHz.
Intel Chipset "I don't remember what".
1.5 GB RAM.
Windows Vista Home Premium SP1.