I'm having this problem too, Slimjet is extremely slow and seems to be doing some I/O work because browsing files on my computer becomes slow as well once Slimjet starts to lag.
Very annoying, and makes IE look like a good browser to be using
Another user in another Topic has mentioned that performance can be improved by using a Custom Cache Location. This is similar to clearing the cache but it has the bonus that you can locate the cache folder to a drive that has faster I/O than the default drive location. If you only have one HDD it may benefit to set the cache folder onto a fast 3.0 thumb drive (if you have a 3.0 USB port). I might be over doing it but about every 3 or 4 weeks I set it to a new folder and delete my previous custom cache folder.
For those of you who wear aluminum foil hats, the voices lie, don't believe them!
Mostly my replies are about Windows OS. If not I try to remember to specify Linux.
Thanks for the input, so does it alleviate the problems to use a custom cache folder? I've already moved Slimjet to the same drive as Windows is on (using portable version).
If putting the cache on a thumb drive helps, then I should be able to get rid of this issue by getting an SSD tho, right? Since it usually speeds up the entire OS.