Really, we need to know the rest of the system specs so we can offer good advice.
As for the question: as long as you remember the possible problems of crossfire (read the FAQ at the top of the Forum page) it's a very good deal and should easily hold up for a year , if not longer.
Also bear in mind the HD4850x2 runs hot and can be noisy, do not install it in a case that has limited airflow or you are asking for problems.
I would, however really advise you to go for the HD5850 if you can afford it, it's quieter, uses less power and most of the coolers exhaust their heat out of the case, so you do not need a case with howling, cyclonic airflow to keep it cool.
+1 5850 4850X2 is too long and may not fit in your case. 5850 DX11 New 40nm Eyefinity ... They should perform on par with crossfire games but the 5850 will rocket in single GPU games. And last thing, 5850 will oc like h e l l to 1Ghz, 4850 you wont even get 50 mhz extra due to heat and 55nm
If I am not mistaken the 4850X2 only has 512MB of memory available because it is crossfire on a card (I believe each GPU uses it's own 512MB of memory, which is cloned). Since you are running at 1900x1080 you want at least 1GB of video memory to be able to turn on all of the eye candy. So I would recommend just getting the 5850 now instead of later