Cool,i understand,nice upgrade.
I have a 5870 and yes they still play most games at 1920x1200 with high settings,i have had 5870 crossfire twice now.
First time was on a rampage extreme with qx9650 and i sold my second card to a guy on here soon after as it was basically sat in my rig unused as my cpu was not powerfull enough,and was poor as well
Second time was just before christmas and wow what a difference with an i7,wow,only sold it as wanted to max out my sons pressents at christmas.
I just checked my photobucket to see if i still had the screenshots to compare x8 lanes vs. x16 lanes,must of deleted the shots though.
Did find a shot of 5870 x-fire on my rampage extreme with qx9650,scored 27k on the gpu as opposed to 34k (check sig link)on my i7 rig,big difference.
If i ever see another 5870 for the right price and ive got the money id have one again for crossfire.
Goodluck with the new build anyway.