FWIW: my girlfriend had 2x2048meg DDR2-667 laptop memory modules lying around that she didn't use, so I swapped my 1x2048meg DDR2-800 module for those. The only benchmark I've done is running WinRAR's built-in benchmark (x64 version, 3.92, multithreaded). Dualcore Core2 P7350
Performance went from ~1060kb/s -> ~1020kb/s... that's a 3.77% performance degradation, even though the RAM is theoretically 16.63% slower. OTOH the system should be able to take advantage of dual-channel memory, but then there's also the module latency
to take into consideration - I haven't checked the latency of the modules.
Are you be able to feel a less than 4% performance drop? It's nothing, and compared to hardly ever hitting the pagefile because there's double the amount of RAM, more (but slower) memory is a clear benefit for me.
Different apps have different requirements, but even in the performance-critical apps, I dunno just which requires insane RAM bandwidth
- as soon as you have heavy processing and aren't just moving data around, bandwidth is less important. And that of course also depends on CPU speed.
YMMV - but if you can get more but (slightly) slower RAM cheaper than less but faster, I'd go for more-but-(slightly)-slower.