15 inch wheels..better bang for the least bucks ?

I was considering getting 17 inch rims but i rectently talked to a friend of mine down att he track (runs a GSR engine on his civic with type R internals) and he told me that the smaller the rim the better time i can get...I've modded my civic down from a 17.4 quat. mile to a 16.6 since adding my exhaust and intake and poppd on some yokohomas...my dorp also increased my traction like a mother...but I was wondering if I should go with 15 inch rims..right now I've got my stock 16's on there...but I'd like to run at least a 16.4 until I can get my headers and cam gear out of the way. Any opinions on whether I should go with the 15's ? Also..I if i do go with 15's i'd like to get the SI rims...anyone know of any other good rims? Thanks guys. If you have pics of SI rims on a red car, please post them. Thanks.