I think 650 will be fine, i run a similar system from a 750 thermaltake but I have an extra video card (2x540s) and 3 extra hard drives
computers draw power, the psu doesn't "push' power, so yes its safe to run any size you want, as long as it can keep up with demand

long story short, run a 2kW PSU if you want, your computer will only draw what it needs

I cannot recommend Silverstone PSU's enough.

PLENTY of grunt (the 850W PSU has something like 70-72 amps on the +12V rail)
Reasonably priced, and a mate of mine who abuses the ass out of his parts (there's OCing your hardware... then there's OCing it and leaving it in a timber cabinet while you're at it...) has only just had to retire a 650W PSU that he's had for 6-7 years (at one stage running two OC'd nVidia 7800GT's, a P4 and about 6-8 HDD's)

not sure what you're referring to as far as 'over-supply', but if you're thinking it might be along the lines of 'too much wattage' it's as teq said...

Also, if you're after a rough guide (and I can't say that I've used any lately, but I certainly did when I was building my last system) google about for 'PSU Calculators' and don't rely on just using one, hit a few and see what your likely power draw is.

Big killers (if not over-clocking) are running multiple video cards and then tonnes of storage devices. If you're not planning on OCing, the only really 'hungry' device I see there is the video card. ~650W SHOULD cut it, but in my experience (which is more my opinion) won't leave you tonnes of room for loads of extra hdd's etc.

Corsair HX650 - just a great PSU

Not for me, but it isn't that bad, luckily taste is subjective

'too much wattage'

Fuck I hate this Americanism.

It's 'too much power'. (Power is measured in Watts).

Even worse, 'amperage' - fuckn really, America!? Really!?

It's 'too much current'. (Current is measured in Amps).

m3nt4l, can you imagine the dust that would collect!?

Fuck I hate this Americanism.

It's 'too much power'. (Power is measured in Watts).

Even worse, 'amperage' - fuckn really, America!? Really!?

It's 'too much current'. (Current is measured in Amps).

Really? You think that power is a better word for describing electrical energy than wattage? The purpose of language is to convey meaning, which word do you think more appropriately conveys the intended meaning?

It's probably not even an "Americanism".