Coolermaster has unfortunately had a bad reputation for PSU's, especially older models. So I would upgrade that first, before you get a new GPU. The PSU you suggested would work great.
As for the cards, your links lead to different things. THE XFX link leads to a 6870 and the HIS leads to a 6850. If that is the correct comparison you are going for (6870 vs. 6850) go with the XFX 6870 100%. It is faster and better in almost every way and can be overclocked to keep it even further ahead.
If instead you mislinked and its in fact both 6870 cards, Either one will do. I would suggest going with the cheapest one and the one that offers the best warranty in Europe (don't know what it is over there).