Wheels & Tires - need offset help

i have some 295/50/15 drag radials that i want to put on my car and i am looking at rims right now and i found some 15x10 summit racing fast five polished wheels with correct bolt pattern but it has a 0mm offset option with 5.500 inch back spacing and a +25mm offset option with 6.500 inch back spacing...i currently have 17x9 american racing rebel wheels with 245/45/17 front and 275/40/17 rear and these new rims/drag radials would be my track wheels but i dont know which offset/back spacing to get or even what the difference is really. can someone help me out so i dont buy the wrong ones?

Those Summit wheels are going to be almost as heavy as the 17s

If you are hell bent on getting them you need 7.5" of backspacing for a 15x10