check to make sure you are actually getting the quantity you requested. Lots of people are having this issue I've noticed, but it is in beta. We have been cancelling the jobs to clear the jobs. we find that we get the order done, but due to rounding issues it has 1 raw resource left over and when you cancel the job you get that 1 back.
most important thing for you is the amount and that it works .. memory speed is not the most important thing for you to be honest ... why ? well having 2-3 ms or worst case even 1 second longer loading time means nothing really for you .. So ddr3 or ddr4 and the amount it can store is the most important thing =) .. and it working of cource