Anything I build will be a consderable step up.
That is so true.
You can compare new CPUs across a wide range of application benchmarks over @ Anandtech.
Compare the i7 860 and Phenom II x6 1055T
. And also compare i5 750 with Phenom II x6 1055T
as those cost nearly the same amount. You might want to also compare the X3 720 and X3 440 with the Phenom II x6 1055T just to cover all your best value options.