More cores & more beef

The RAM doesn't matter that much, it's the hardcoded CPU assist that matters. So if you want full performance, don't save on the CPU.
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?
Windows 7 x64 usually between 30-55%. I did try the latest KopiemTu 1.3 but had slower hashrate than windows, I mined on simpledrk.com and found Linux gave me overall less hash/shares.
I have also recently bought 6x750Ti on H81 Pro BTC, G1820, 4Gb RAM and no issues with performance mining JPC. CPU usage: 40-60%
Main problem I have is Win8.1 x64 mining Scrypt-jane or Scrypt-n. Max 1.7 kh/s per card (yacoin) or 115 kh/s (spaincoin).
On the other side I have old SATA disk with installed WIN XP 32bit where I achieve much better results: 3.750 kh/s (yacoin) and 155 kh/s (spain) per card on the same system.
Also for x11 and JPC I'm getting lightly better hashrates (2-5%) with win xp.
Don't know why this happens, but will try windows 7 in a few days.