find out what your motherboard supports, most of them only go to 1600 (highest), and may not support higher ones such as 2000.
Now I have 1330 Mhz with a Cas latency of 7, and I have 7.3 for ram on windows index. It's pretty fast so I assume 1330 would be fine for you.
note: Cas Letency is the amount of time ram used to gather data. The smaller cas latency the better.
for instance, if you had 2 ram cards. 1 with 1330 Mhz and cas latency of 7, and the other with 1600 Mhz with a cas letency of 9. You would want to go with 1330 Mhz one.
Mhz is just amount of power is uses working (usually higher is better, but no in the ram case)
hope I helped
---------- Post added at 10:17 PM ---------- Previous post was at 10:16 PM ----------
Not really. It depends.
I have 1600 MHz DDR3 with a CAS Latency of 9 and i get 7.5 on WEI.
If you mean the other WEI scores, then
CPU : 7.4 - Phenom II x4 980
RAM: 7.5 - 8GB Corsair Vengeance
GPU: 7.9 in both - GTX 560 ti @ 1000MHz
DISK: 7.4 - Corsair Nova 2 60GB SSD