Hopefully this will give an indication.
I ran the FSMark07 benchmark against the old and new systems. Both systems were configured as per NickN's excellent instructions, OS and FSX, with the exception of AA. I could not use that on the old system. FSX settings were also set the same on both system for comparison purposes.
Here are the details for the old system:
FS Version FSX SP2 DX9
CPU P4 3.2 Ghz
GPU 7600 GS 512M (178.24 driver)
Memory 2GB DDR2-400 @ 400MHz
Motherboard Asus P4P800 Deluxe
Sound Integrated (ASUS SoundMAX)
AA/AF No AA 16x AF nHancer
Resolution 3540x1024
Screen Mode Full Screen
OS Vista 32 SP2
Add-Ons FSGensis, Traffic X, UTX, GEX
Settings See screen shots
Min FPS 5
Max FPS 18
Avg FPS 9.9
Cores operating 1 + HT
FrameLock 30
And here are the details for the new system:
FS Version FSX SP2 DX9
CPU i7 @ 2.8
GPU GTX 260 Maxcore
Memory 6GB DDR3-1600 @ 7-8-7-20-1600
Motherboard Asus P6T Deluxe
Sound Integrated
AA/AF No AA 16x AF nHancer
Resolution 3540x1024
Screen Mode Full Screen
OS Vista 64 SP1
Add-Ons FSGensis, Traffic X, UTX, GEX
Settings See screen shots
Min FPS 16
Max FPS 31
Avg FPS 29.9
Cores operating 4
FrameLock 30
I also did a run with the FrameLock set to unlimited on the Core i7 system which resulted in these frame rates:
Min FPS 27
Max FPS 61
Avg FPS 41
The FSX settings I used were the best I could do on the old system. Keep in mind I used the same settings on the new system for comparison purposes:


Note: The Target Frame rate in the above screen capture should show 30, not 20. Took the wrong screen capture.



The frame rates in the following graph were obtained by averaging the results from five runs of the benchmark for each line:

If you have an old system and are considering an upgrade, the Core i7 is certainly a good choice.
Keep an eye on the Tweaking and Overclocking forum. I'll be posting the results of OC'ing the i7 there soon.
Regards,
...jim