None of the Phenom IIs are worth £300 (cpu+mobo) more than your current setup. You'd be wasting your cash.
If you're desperate for performance now you could get one of the newer C2Qs or upgrade to i7 now.
None of the above is any real leap on your current performance though. Whether it's a higher clocked C2Q for £200+, a phenom II for £300+ or an i7 for a kidney and an iris.
Yes you'd get a better system, but nothing significantly faster than a Q66 at 3ghz; save your money for one of the next generation of i7s.