I've responded a few times on this question, on DDR3-1333 CAS 9 mixing two sets of 8GB/stick density works 90%+ of the time. The F3-10666CL9Q-32GBXL kit is a better option for 32GB. I 'get' the cost difference so you'll need to weigh-in if $25 is worth the aggravation.
Thanx for your reply! I already have a system with G.Skill F3-10666CL7D-8GBRH (2x 4GB) and I want to add G.Skill F3-10666CL9D-16GBXL (2x 8GB). So the cost difference is a bit bigger. Is 90% for this setup also realistic?
Asus p8p67-m pro
G.Skill F3-10666CL7D-8GBRH (2x 4GB)
Windows 7 64-bit
What I would like to add:
G.Skill F3-10666CL9D-16GBXL (2x 8GB) (€ 105)
My oversight, probably won't be in my top choices. The RH and XL are completely different IC's not to mention totally different CAS. Trust me, I 'get' you can run the RH's @ CAS 9. Further, I'm not a fanboy of mixing densities either.
So, can it work sure ... can it run reliably maybe. You are now an 80/20 to having 24GB working reliably.
If it 'my' rig, I would either re-purpose or eBay or in a drawer the F3-10666CL7D-8GBRH. I don't like potential problems hanging over my head nor a multi-hour job going poof...
You ask 10 people you'll get different answers. On my servers even with ECC I don't mix-match density, CAS, type, IC's, etc.