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Those won't fit, chief - you'd need almost a 4" spacer to make it work (with stock trailing arms). The biggest you can fit with a stock trailing arm is 17x8 with 4" backspacing, -11 offset, 5x4.75 bolt circle - American Racing part number 505-7861.
It depends on how much you are willing to mod your car. Check out Groovyjay's setup - he's running 20"x10" rears with 285/30/20 Pirelli P-Zeroes.
His site is listed here - http://www.corvetteforum.net/c5/groovyjay/