You will rarely have luck going up.
1. Always buy a full set of RAM in a single package ... if your ...
Mobo is dual channel, buy 2 x X GB
Mobo is triple channel, buy 3 x X GB
Mobo is quad channel, buy 4 x X GB
You have no warranty for any pairing of RAM that didn't come in a single package.
If you putting 4 sticks in a dual channel board, again buy a 4 x X GB package .... not recommended. 2 x 16 GB is better than 4 x 8GB. CPU overclocking is easier with 2 sticks than 4, memory contoller has to wok harder with more sticks.
2. If ya didnt do any of thet... you wanna match as many thungs as possible... Brand, Model, Speed, CAS. OEM suplier version. Using same vendor is not a guarantees... even same model as they often switch OEMs in later versionbs.
3. As above
a) in your position read the SPD of the lower speed / higher CAS RAM, better yet take a CPUz screenie
b) go into BIOS And lower the speed, raise the CAS to match the slower RAM manually.
c) I have had two sets of RAM with exact same brand and model and speed rating but withdifferent OEM suppliers and 10-12-12-28 and 10-12-12-31 ... no matter what I did, could not get them to play nice. yet ,,, matching a different brand different model no. but with same OEM, speed and timings worked oin 1st boot
d) If step b) doesn't work, increase DRAM voltage a bit....rinse and repeat till it works... be aware on manufacturers voltage limits.
