5670 x2 or Single 4850?

HD5670x2 beats the HD5750 and sometimes the HD5770, depends on the game's scalability. However, I'd just grab an HD5770 and crossfire that later.

Any difference between the saphire 5770 standard and the saphire 5770 vapour-x

The Vapor-X has a slight overclock I believe, and it has better cooling.