If you decide to raise your limit I have these for $700 shipped. http://www.s197forum.com/forum/showthread.php?t=117059 Already mounted, balanced, and have universal tpms that works with both styles for Mustangs.
Another option would be 15x8 wheels with 275/60/15. You could get the wheels and tires for around $500 if you aren't picky about the wheels.
Thanks for the offer. What 15x8 do you speak of because racestars or sve drag wheels add up once paired with drag radials.