Computer rebuild, Rome: Total War is slower

I have been a long time fan of Rome: Total War, and have spent way too much time playing it. It always ran on my old E4400 rig with only a little slowdown during large battles or while looking sideways at my entire army. With the release of the Sims 3 and Empire, I decided to rebuild my rig to help increase its longevity.

My new specs are:

Intel i7 920
Gigabyte x58-UD3R
6gb Corsair XMS3 DDR3 1066
HD 4870 1gb
WD sata 3.0 gb/s 320 hd (same as before)
PC Power and Cooling Silencer 750w

I went into a quick battle to see how Rome ran, and it runs worse than before! So, I ask the following:

1) Is Rome optimized for quad cores (I doubt it due to it being so old).

2) I thought this game was very cpu dependent - my E4400 was 1.8 ghz - the i7 920 is hyperthreaded 2.6 ghz...so that should merit an increase, right? Unless it's not utilizing two cores like a C2D would...My copy of Rome is patched to 1.5.

Any help would be greatly appreciated!