Well as i say every time on posts like these and has been said several times over the many posts here about PSUs: Price=quality.
The £40 one i will put several quid on it that the ampage across the 1V rail(s) is low, so will not power nothing it says it will too well. It will also be uber inneficient and hot and probably likely to blow damn easily in comparrison to a more epensive one.
The 750W would be better because:
1. It will easily power it
2. It will be at around 60-70% usage, which is the point at which power supplys are most efficient
and 3. it will allow for upgrades to the system without taking any strain.
The 750W one is good indeed, but i would deffinately advise you to look into corsair power suplies for the following reasons (and this kind of thing should be a sticky, i'm sick of hearing myself say it
):
They are, so far as i know, the only mannufacturers of power suplies that test their units at the stated rating at 50 degrees, most others do it at 20 degrees. This helps to ensure reliability.
They all come with 5 year warranty.
They all come with a single dedicated 12V rail. This makes the system give cleaner power at higher strains and makes it more efficient.
All of their units are over 80% efficient from 20%-100% usage, so regardless of how you use it, it will be VERY efficient.
They are a little more expensive, but refer back to my "price=quality" statement before, this is true all over power supplies. A 750W one will set you back about £100, here is one that i have found online:
http://www.scan.co.uk/Products/750W-TX-Corsair-PSU-single-12V-rail-quiet-and-cool-80plus-Eff
(i have used scan.co.uk before, they are VERY good). You can get an 850W one for an extra £13 aswell, but they are very very very good supplies. deffinately think about it if your budget allows for em.
Also, they have been proven to work ABOVE what they state. I have heard of people that have used a 500W one at about 550W one with their system still bbeing totally stable. I don't think i would want to do that though, wouldn't be good for the power suply, but good to know they are that robust
