Do you mean the Core 2 Duo or a dual core ?
The performance of the new Core 2 Duo is very impressive apparently but I havent tried one yet.
I did recently replace my 660 P4 3.6ghz with HT and 2mb L2 cache with a dual core D945 3.4ghz no HT with 2mb L2 cache on each core.
The only program that I have that maxed out the 660 was a video converting program and as I posted in another thread how the 2 CPUs compared.
Here are the results of converting a 4 Hr 52 min mpg film of 6.58 gig to 4.29 gig Xvid using Auto Gordian Knot
660 Total time: 6 hours 3 minutes 46 seconds
D945 Total time: 4 hours 25 minutes 21 seconds
The difference between your P4 2.8 and the D945 would be even greater.
My motherboard wouldnt run the new Core 2 Duo and the D945 is ridiculously cheap at the moment in the UK, I paid £98 inc vat for it from ebuyer.com, my 660 is currently selling for around £270 in most on line stores.
I paid £208 for my 660 in march this year and the D945 was over £300 at that time