Well... I don't know where to start

Originally I bought PrimoCache because I was a fan from Fancy Cache, it did wonders on machines with low amount of ram.
And when PrimoCache was released, I bought it as soon as I noticed (usually I checked once my fancycache serial expired)
But then I bought an i5k haswell with 16gb of 2.4ghz ram and primocache was like scratching his belly. Primocache almost did nothing even if I didnt power off the pc for days.
So then, I changed my licence to my 1st gen i3 laptop (now i5, still 1st gen)... but I'm using Windows 8 in this laptop.
The problem is that... in some circumstances, having primocache were better, but some others were not. Win8 seems very jelous of the available ram, at least with too a low amount of ram (I still have 3gb), so in the end I deactivated PrimoCache.
From time to time, I think the best I can do for this computer (besides buying an SSD/RAM) is to have a persisent cache in my HDD.
I can do that with primo if I make a partition for it... and my question is, what would be better ? an L2 on a partiton on the HDD or having a high speed usb flash drive for L2 ?
PD.- I haven't used PrimoCache like for a year, maybe they have improved performance over win8 with this new version ? Or maybe I should go back to win7.