Which is better higher Mhz or Gb?

Solution
What do you do with the rig, in general more is better, but if you don't have the requirements, I.e. not much multi-tasking, not use lare data sets, the their are times where the faster 8GB might trump slower 16GB (generally not often, but there are times 😉 )
More capacity means a larger drive-cache, and I think 12GB is the diminishing return for most users. At any rate, RAM by the bandwidth is so cheap these days I'm more inclined to say speed, just buy enough for your use.
 
What do you do with the rig, in general more is better, but if you don't have the requirements, I.e. not much multi-tasking, not use lare data sets, the their are times where the faster 8GB might trump slower 16GB (generally not often, but there are times 😉 )
 
Solution