Could you tell me which exact inf files should I replace

if you were able to had your 5+ GPUs running in one rig with win7 64bit then you must have used the modded inf files afaik.
i believe that this was the thread i got the modded *.inf files from:
https://litecointalk.org/index.php?topic=11761.0it says that it ONLY works wit 13.12, but i swear i just installed the 14.6rc2 Drivers, used the modded inf, and all GPUs get detected.
Indeed , I Installed 14.6 RC2 , and one of the cards was with an error on the device manager. After that downloaded the 13.12 drvs from techpowerup , and just ipdated the damaged card with 13.12 ver of the driver and now its fixed , 5x280X GPUs on 4.277 MH /s on X11