I have the MSI Twin Frozr, before they came out with the Gaming series. It isn't as loud as some I suppose, but it certainly makes noise when it spins up to max RPM's.
I'll look into that Prolimatech MK-26, looks pretty nice. I tried one of the replacement heatsinks before, on a video card, and it seemed rather risky for the installation, almost touching components. Also, it didn't cool the ram, and there was no room for decent ram heatsinks after adding the gpu heatsink. I think it came with tiny little heatsinks for the ram that looked barely enough. Maybe this one is better though.
I got a Define R4 case, and I love it! It's no Silverstone FT02 for airflow, but for silence, it's almost inaudible, even with a cheap Corsair CX600M power supply (120mm fan). I have the internal fans set to 7v, the middle setting, and it seems it doesn't make hardly any noise. I'm liking the 140mm fans.