Ram for an APU

I remember hearing from multiple places that when deciding on RAM for an APU, you need to make sure you have a certain amount of something, or it would slow the APU down, but I don't remember what the was. I don't remember if it was CAS latency or timings or clock speed or what it was, Could someone please refresh my memory (no pun intended)?

ram frequency (higher is better) and cas(lower better)

I know that, generally, that's how it is. But there is something specifically for APUs that is a big deal if something is not high enough or too high or something. A big deal, as in, it would slow down the APU if you bought the wrong ram.

hogher is better as far as frequency, find some ream that is ddr3 2133 and cas 9 and you'll be good

Yeah, the effect is felt much more with APU's because it uses the system memory as video memory. Generally I recommend 8GB of 1866MHz memory with a 9 cas latency.

you can get case 9 2133 ram pretty cheap now too, 2400 would be okay price too if they sold cas 9s in anything but 4x4GBs sets

8GB with 9 cas at 1866MHz is ~$35, at 2133MHz ~$55. Up to you if you want to drop the extra cash on it, but its a decent bit more expensive.

$35

 with no rebate, promo or combo and with free shipping? where?