How much Power do I need

Well you could list your planned specs and we can tell you.

or

Just set all your desired specs into this calculator its a very good real power calculator.
http://extreme.outervision.com/psucalculatorlite.jsp

Make sure when you do figure out how much power you need get a good quality brand Corsair and Antec have some of the best power supplies around.

^+1

Getting the wattage needed is half the story, what they don't tell you is the amps. Corsair and Antec have PSUs with mad amounts of available amps, 3 or 4 times as many amps as lesser quality PSUs of the same or even great wattage.

For example I've seem 750W PSUs with only 30A, while my Corsair 750TX has a whopping 60A

I am looking to get a Thermaltake case so I was going to get a TT PSU are they considered in the same class as those 2?

thank yoy for the link

I've never heard of it, and googling "TT PSU" brings up all sorts of things about it being a PSU for turn tables...

EDIT: this? http://www.thermaltakeusa.com/Product.aspx?S=1207&ID=15...
If that one it looks decent enough... if you pick one just provide a link so we can look at it's specs

Thermaltake have some great power supplies but depends where you get it because its usually overpriced IMO.

The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the +12 volt rail(s) can easily power a system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the +12 volt rail(s) can power a system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5XXX series cards which use less power due to their energy efficiency and the new Nvidia GTX480 which uses a lot more power.

A high quality 500 to 550 watt psu will have a +12 volt rail rated at 40 amps. A high quality 700 to 750 watt psu will have a +12 volt rail rated at 60 amps.

In addition the power supply should be at least 80+ Bronze certified for energy efficiency. There are some models available which have achieved 80+ Silver and 80+ Gold Certifications.

Before purchasing a new psu you will need to decide whether you will eventually have a pc with one or two video cards.

Corsair and Seasonic are two brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units. One example would be the newer Antec power supplies.

The reason I am looking to upgrade is because I planning to use crossfire of 2 XFX ATI 4850 and I am looking to install the Thermaltake Big Water Liquid cooling and I think that both of those (especially the water cooling) require massive PSU power

 
You really dont want Thermaltake water cooling.

Please expand on that because I am literally just about to buy it

Best answer selected by redwing3139.