If your talking about the card pictured below...
1) PowerColor are a value brand, but the R9 290 is very fast, on par with a GTX 780.
2) £175 is a very good price indeed, new they retail at £280+
3) It appears to be a reference card, so will run very hot & be very loud. However, you should be able to buy a 3rd party cooler like the Arctic Accelero Xtreme III(http://www.tomshardware.co.uk/r9-290-accelero-xtreme-290,review-32828-2.html) and improve it a lot, if your up to that, technically.
4) It will be pretty much identical in performance as the OC isn't that substantial. If you get a reference card like these are, you'd need to replace the cooler with something better or stump up for a non-reference 290.
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