Originally Posted by NASzi
I know flowrate plays a huge part, for the past couple of months I had my MCP-655 set on 2, my 2500k @ 4.8 would always max out at 63 while doing some intensive gaming (Borderlands 2 mainly), I ramped up the speed to 4 a couple of days ago and my processor started hitting 66 while gaming. I'm guessing the water isn't staying in the radiator as long so it isn't getting cooled as effectively. Just a thought.
Not doubting your experience of a hotter CPU at a higher setting - I don't doubt you've actually seen that.
It's not possible that the cause is higher flow. If the water "spends less time in the rad" then it also passes through the rad more often. Say the water is spending 10 seconds in the rad, and circulating completely in the loop every 30 seconds, so the water is spending one third of the time in the rad. If you double the flow, the water would spend 5 seconds in the rad, and circulate completely every 15 seconds - still spending one third of the time in the rad.
Higher flow would normally improve the ability of the waterblocks to dump their heat into the water, since higher flow leads to turbulence and mixing in the boundary layer in the blocks, helping the heat get into the water.
Don't know why you're seeing something contrary to that, but it can't be the higher flow.
I would conjecture that it could be heat dump from the pump, but it seems like it would have to be an awful lot of heat dump to make a 3c difference.