Appropriate Wheel Offset for 18" Wheels?

So, I know this is kind of cheesy but I made a mock up wheel out of cardboard to see what offset I'd need for the rear. It's just a cut circle with a rectangular piece taped to the circumference to simulate the width of the tire. I measured it on both sides of the car just in case my perches weren't centered on the rear axle. The wheel is cut to about a 245/40/18 tire (may be a tad taller and wider). Overall, I got that I'd have at least if not more than a finger's worth of room on both sides (leaf spring to outer trim) with about a +7-8mm offset. I measured 130 mm from the outside of the inner "tire" cardboard to the inner face of the cardboard. 245mm/2 = 122.5mm -130mm = 7.5mm. To use a max of a 1/4" spacer I have to find a wheel that offers a minimum of a +30mm offset for the fronts and about a +13-14mm offset for the rears.

So far the wheel that may fit my description on Summit is:
http://www.summitracing.com/parts/dgw-22786/overview/
http://www.summitracing.com/parts/dgw-22783/overview/

The Enkei PF01 is offered in +15mm, +35mm, and +45mm +with the 9.5" wide wheels. I'm not sure if they'll fit even though a 245/40/18 will still mount to them. The center bores may have to be bored out to 73mm as they're tapered:
http://www.summitracing.com/search/brand...mp;autoview=SKU