i thought you were talking about desktop quad cores, the difference now is a lot less now that your talking about notebook hardware, where intel will give you the edge if you split the cores due to their faster architecture... you can go either way at those clock speeds - i'd say go for personal preference especially if the i5 has ht (though i don't think the notebook ones have. i'd still lean towards having more cores, theres less likely a chance the system will hang at times some cores are being used because theres obviously going to be more free cores
(sory it took so long to respond, toms email feature, among other features, is not working right now so i had to search for this thread)
let us know what solution came about for you and your satisfaction level with the new comp. it'd be interesting to know how it worked out for you