Can I mixed use of the F3-12800cl9d-8GBRL and F3-12800 cl9d-8GBXL on GA-ep43t-ud3l?

[piiicoppermine]

Can I mixed use of the F3-12800cl9d-8GBRL and F3-12800cl9d-8GBXL = 16GB on GA-ep43t-ud3l?
CPU QX9650 c1
What's the difference between these two models?

I'd tried F3-12800cl9d-8GBRL on Asus P5P43TD pro. Needn't to add voltage on N.B or ram on FSB 400 (1600 O.C), but the M/B isn't good for OC, no Vdroop control.
I don't know why, but if FSB 400, it can only run 8.5x stable without adding voltage to CPU/RAM/N.B/S.B. It doesn't make sense, if it runs ok on 400x8.5, why it can't run 400x9 (9x is the default FOR QX9650)) without adding voltage? (I've a good HS + fan, Deep cool - gamer storm)
Then I moved to GA-ep43t-ud3l. Then the F3-12800cl9d-8GBRL is out of stock, only F3-12800cl9d-8GBXL available, I don't know if I can add this pair and mix with the 8GBRL on my new M/B.

What's the best setting for these ram in this BIOS - ga-ep43t-ud3l f9 (FSB 400 only, 1600 OC)?

[Tradesman]

The X series is designed w/ the P67 in mind, not positive if they are using a different IC on the sticks or if the difference is only in the programming. Gskill should be able to answer Monday

[GSKILL TECH]

Just wait for the 8GBRL.

As far as raising voltage, only NB Voltage may need to go up a little for 4 modules, but that's it.

Thank you
GSKILL TECH