What psu should I buy for my setup?

It depends on when you buy it, PSU pricing appears to be pretty volatile right now.

Single Rail @ 400W minimum with a known good name brand PSU.

PC Power and Cooling
Corsair HX, VX or TX series
Antec Earthwatts or NEO series

There are others.

Post your choice just before you buy and get feedback.

I'm pretty sure this is what I'm using on my old computer right now

OCZ Modstream 450W
http://www.bcchardware.com/index.php?option=com_content...

Would this be substantial enough for overclocking?

I found a good deal on newegg, an OCZ EvoStream 720W for $80. Keep your eyes open, and follow this list of tiers.

http://www.tomswiki.com/page/Tiered+PSU+Listings?t=anon

Hmm, it's a shame I can't buy from newegg since I live in Canada.

But here's what I found so far:

OCZ GameXStream 700W $126.81 - $40 Mail-in rebate
http://www.ncix.com/products/index.php?sku=18185&vpn=OC...

and

OCZ EvoStream 720W $219.99 - $25 Mail-in rebate
http://www.ncix.com/products/index.php?sku=22037&vpn=OC...

Should I dish out the extra money in order to get the Evo+20more Watts? They are both under the same tier, but I guess the Evo is slightly better?

Your pretty sure?
Is the review up to your standards? If so, then it is substantial enough.

Something to consider is how long you have been using the PSU. As the capacitors age the PSU is not able to deliver as much current/wattage.

It's also a tier four PSU.

You shouldn't have any problems, but if the machine is flaky under load I would change the PSU.

OCZ has some great PSUs, good PSUs and some low end PSUs. They're one of the manufacturers that you have to know which PSU and then check reviews. Modstream is low end, StealthStream is mid range, GameStream, EliteStream and Evostream get good reviews. The GameXStream you listed is a good PSU especially for the CAN$ price. In short terms i'd agree with Zorg and run what you have unless/until you have stability problems and then change the PSU.

I recommend Seasonic PSUs. They also manufacture the PSUs listed above.

I will definitely give it a try, but it seems like I will just be making another trip to the computer store to pick up the bigger PSU. Not that it really matters since it's only a 5 minute drive  

Do you think it's even possible for a 450W ModStream to support those specs? It's low end as listed in the tiers and low watts. The other guy suggested I need a 720W PSU, I really doubt my old 450W will hold up, but nonetheless it's worth a try.

If anyone has any other opinions please feel free to add. If my 450W doesn't hold up, what is the minimum watt PSU I should buy?