What are the limiting factors for FSB speeds on 680i?

[Viper GTS]

From the searching I've done most people seem to get 400+ FSB speeds quite easily (1600+ QDR). I have my E4300 running happily at 3.2 GHz (1423 QDR) with my memory at 800 MHz so I figured I'd try for 400x8 with the memory set to link/sync. I can't even post at anything higher than 1300 or so set that way, even with the multiplier set all the way down to 6.

Is MCP cooling a limitation? Obviously the CPU and memory are easily capable of the speeds I'm attempting.

Viper GTS

 

[PCTC2]

you want your memory set to unlinked. The linked setting often pushes the RAM too far out of specs to run.
At my current clock speeds of 3.55GHz, link/sync on my eVGA 680i tries to run my DDR2-800 @ 1100. Set to unlinked and set the memory speed and timings manually.

 

[Viper GTS]

1600QDR results in only 800 MHz memory speed. My memory is only 667 but it has been running fine at 800MHz (and I can still set the timings even when set to link/sync).

Perhaps some faster RAM would help it, I'll try to get my hands on some to test.

Viper GTS