Uhm... With watercooling you're getting 46-52? Thats crazy....
Well, if you really want a watercooling setup, I'd recommend that you do your research thoroughly. There are a few companies offering peltier cooling out there, but they aren't cheap (not a problem to you), and they suck up alot of power (might be a problem). You will probably need a second power supply, or get a new 1kW monster PSU to power that thing, and an SLI configured computer.
It will still require watercooling, and from what I gather, it might be a good idea to add another radiator. And it will only cool the CPU (getting GPU units will require yet another power supply).
Anyway, here's a link to an Australian site selling TEC coolers.
http://www.pccasegear.com/prod3047.htm
Price is AUD$750. (includes the watercooling kit).
You can make it yourself, but remember to waterproof the area. Which is alot of trouble, I got some websites saved on my HDD from the last time I looked into TEC cooling on how to waterproof your CPU, and install a TEC under your watercooling system.
Making it yourself will undoubtedly be MUCH cheaper, all you need is to make sure you get a 200W or better peltier (I'll suggest you get at least double the watts your CPU uses) and stick it under your waterblock. They're pretty thin, and there's a seller on ebay that sells peltiers. Too bad they ship only to the US.
Phase change I've personally never really looked into it cos it costs way too much. If you can afford it, and afford to run it, why not? I'm not sure what it'll sound like, but I've got a feeling it isn't very quiet.