Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
happymedium is right, don't bother "upgrading" to any of the 69xx series or anything - your 5850 is still comparable to any 6870 and getting 2 5850's would give you more of a performance boost then a single card when you're gaming at that kind of resolution.
You can find a ATI 6870 for cheap on Newegg.com these days. For about the price you're looking for. I have the XFX 6870 Black Edition and it's cool... quiet... and powerful.
I think the 6870 is more overclockable then the GTX and a lot more quieter/cooler - maybe ~4-6% increase in performance...