Already have a hd5770 looking for getting another one or a hd5850

Here is the thing, i have made my first custom build rig and its now running nicely for 2 month. At the moment i bought my parts 5850 was nowhere findable and went for a 5770. Now i got a xfx and can run at 1000core and 1350mem in game being fully stable and about 1085core and 1450 mem in bench. Now i have mostly paid all my stuff and i might look for a 60gb ssd or 2 30gb and put them in raid0 but also adding more gpu power as i will get me some big game like GTAIV and Dawn of discovery and maybe a fps like cod4:mw galatic warfare mod or L4D2 and playing them in 1920x1080 resolution. My psu have only 2 6pin pci connector so if i get a 5850 all my pci connector would be taken and that would mean having to buy a new psu when i get another 5850 in 1 or 2 year to play the game by then. SO does i ambetter off with buying now another 5770 and go crossfire and be set for 2 year and then change everything or get a 5850 now and in 2 year get a new psu to put a second 5850 ?

Spec:
I5 750 will be running at 3.8ghz when i get my new set of memory
4gb of g.skill trident 2000mhz cl9 kit on the way, running at the moment with 2 gb of 1600mhz cl9 g.skill
MSI P55 GD65
COOLER MASTER HYPER 212+ CPU COOLER
XFX HD5770 running at 1ghz core 1350mhz mem
CORSAIR 650TX PSU
ANTEC 200 CASE

Dont be afraid i have made sure i have decent cooling for if i go crossfire way.