You can go 18x9.5 up front with the right backspacing, that is what the Cobra R ran. Hell, you can go really hugeified with a SLA setup up front, like 335 wide hugified... but that's $$$$$$$$$$$$$ to do.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.