PC2700 RAM vs. PC3200 RAM

Does anyone really notice a difference between PC3200 DDR Ram (400MHZ) and PC2700 DDR Ram (333MHZ)? I had the A7V333 Asus motherboard and had the PC2700 RAM in it. I upgraded to an Asus A7V8X, (Mainly to support Radeon 9700 Pro 8X AGP) and also went with the PC3200 Ram. I really didn't notice a difference in RAM speed while benchmarking. If anything I think it's a little slower. I did read that having all 3 RAM slots makes the RAM run at 333MHz instead of 400MHz, so I only have 2 slots filled. 1GBs of PC3200 basically. I still don't notice any difference. Is it really better to have PC2700 or am I just not doing something right in the BIOS settings? Thanks for the help!