I5 430+4570 vs t4400+4650

hello I'm after a laptop to use round the home and at my girlfriends that will not be my main gaming rig (Q6600 oc'd to 2.94 2gig ram 8800 gtx vista) but that would let me do a little gaming + internet. my budget is £600 max which is really a little to much somthing closer to 400 would be better if i could get away with it  

So iv'e found these two one the dell website:

studio 15, i5 430, 4 gig, ati 4570 512mb ram, win7
studio 17, pentium dual t4400, 4 gig ram, ati 4650 1gig ram, win7

both are £550...
or

studio 15, i3 330, 4 gig, ati 4570 512mb ram, win7

for £500

So i would like to know which you all think would be best!
I dont care so much about load times and everyday speed really its all about fps  

Do you think i5 is worth £50 for gaming improvment?
would i be totally killing a ati 4650 by using only 1mb cache t4400