350-550W PSU for this build?

Hey, I was wondering what PSU I should get for my PC that I'm in the process of building.
I was originally going to go for the XFX ProSeries 550W Core Edition, but that was out of stock and Novatech could not get ahold of it, so I'm back to picking power supplies.

I'm planning to overclock my i5-2500k to at least 4.2GHz, and have a ASUS P8Z68-V/Gen3 mobo, with a Sapphire AMD Radeon HD 6850 and am planning to get a Intel 330 60GB SSD.

The eXtreme PSU Calculator suggests around 350W for this system, but I thought it would be good to have some extra wattage for the future (Crossfire when needed in a few years and such)

My budget is £40-£60 (preferably around the £50 mark).

I've looked at http://www.novatech.co.uk and http://www.ebuyer.com and have a list of PSUs that are supposedly good and more or less in my budget, but would like some other opinions:

Antec High Current Gamer 400W
http://www.ebuyer.com/245670-antec-400w-high-current-ga...
PC Power Cooling Silencer Mk III 400W
http://www.ebuyer.com/327894-ocz-pc-power-cooling-silen...
OCZ ZS 550W
http://www.ebuyer.com/264509-ocz-zs-series-550w-80-bron...
PC Power Cooling Silencer Mk III 500W
http://www.ebuyer.com/327893-ocz-pc-power-cooling-silen...
Antec High Current Gamer 520W
http://www.ebuyer.com/245671-antec-520w-high-current-ga...
OCZ ZT 550W
http://www.novatech.co.uk/products/components/powersupp...
Thermaltake Smart Power 550W
http://www.novatech.co.uk/products/components/powersupp...

I've looked at the Corsair PSUs but the ones in my wattage/budget range are of the more mediocre CX Series.
Not too picky about modular vs. non modular, but I'll let you guys be the judge of what to get.

Any feedback is appreciated, thank you.