Hi,
honestly, this sounds like a typical case of overload...
might be the plugin delay compensation (pdc) if its not that, but I bet it is that.
if it comes to fx try to bundle them on aux channels, so that you save instances.
Search this forum for CPU saving or performance tuning to find out more.
Updating to 64 bit is a whise idea, since 4 of the 8 GB RAM in your system are mostly wasted right now.
Hope this helps.