I run 6 x 750ti with 8gb & celeron g1610 never had an issue with performance, it hasn't stopped my cards hashing at full speed....ever.
Linux? How much CPU usage?
I run win7 x64 w 8GB ram, and with 6 copies of ccminer50 running it is at about 45% CPU, and only 1.7 GB Ram being used.
It was a problem before the miner got some optimization, and I had to at least double up the cards because even 4 copies of the program running would put me at 100% CPU.
Do not have any problem at all with it now.
Since he already has the chip in the system I would say no need at all to upgrade, but should that change in the future you could always upgrade then.