Intel Quad-Core is most certainly 4 cores afaik! Those extra cores will only help you if the program is multi-threaded [i.e. can take advantage of multiple cores]. If you want a performance boost for free, you could try overclocking your E6750, as it's a pretty good OCer as far as Conroe goes, might be the best thing before you spend any money.
As a side note, we seem to have loads of people on here from Manchester recently! Haven't seen ya around before so welcome to OC3D mate