Seriously? 5770 is not meant for 1920 resolution gaming because of it's terrible memory bandwidth.
You are joking right? Have you ever played a mainstream (i.e. not crysis, metro 2033 or any other uber demanding games) game in 1080p with a 5770? I can personally vouch that it is enough enough for 2048 x 1152. You can dam near max out dirt 2, I haven't tried completely maxing it as I'm probably pushing 50 fps as it is.
If you weren't joking then please don't give incorrect information to people looking for answers.
To OP I agree with the above post, upgrade your monitor first as a single 5770 is more than enough for your resolution and can sufficiently handle any game at a higher resolution