At Scan.co.uk the XFX 7850 1GB in [Today Only] deal cost's only £124.79, with TWO free games and can be overclocked to [GPU]-925Mhz and [RAM]-1275Mhz, least the one I purchased can be overclocked to that at stock voltage (if I went higher, FurMark started to produce either artifacts or freezes).
And not too loud. In FurMark after 4h was round 70-75 degrees at 70% fan speed.
EDIT : And as for PSU, a 7850 1GB + 4.2Ghz@IB i5 + 3x HDD + 2x Optical drives + SSD (plus bit and pieces like additional USB 3.0 PCIe card and more external USB 3.0 ports), all of this can be happily fed by a 450W XFX.