Well for the sake of anyone who, like me, was researching the same question I had... (Re my last comment) I eventually got myself an i7 4790 from ebay (£150) which according to the benchmark I ran gave me a 40% overall CPU power boost (LGA1150 mobo). Previously problematic projects with multiple midi and syth tracks now run without glitches and dropouts at a reasonable (negligible) latency.
In the meantime I'd found a few websites on minimising latency via altered settings....I found
this one quite useful.
I was also surprised to find that uninstalling an app (AutoMap) that came with my Midi keyboard (Impulse25) was causing more latency trouble than it was worth.
I think i'm fixed for the foreseeable....