Ati drivers have always been fine on xp, and they were only dodgy on vista when it first came out.
ATi cards do run hot, my card and my old 1900xtx run at around 110*C fully loaded, but they can safely go hotter.

Saying i dont like then coz they run too hot in my opinion is like saying this is a motorway but in my opinion i think 30 is top speed.

If its designed for LOL*C then its fine.

The 4890x2 will be teh pro but will also be muchos £.

The 4870x2 is a damn good card.
The 4890 i believe is decent too.

If your looking at spending a significant amount of money but not wanting £lol id go with eitehr a single 4890 or a 4870x2.

Also overclocking ati cards is easy and (relativley) safe, Catalyst Control Centre can do it for you