Good idea to try to stay with stock sizes. After getting the tire/wheel combination info on all the custom SSRs at SEMA, tires to fit the 20/22 combination were difficult to find, expensive, and because they were all Z rated tires, quite soft, and therefore limited mileage before they wore out. Availability of chromed wheels was marginal with the correct offsets.
The downside of staying with the 19/20 combination is the very limited availability of wheels in 19", and even more limitations trying to find the correct offsets. It seemed the only way to work it was with the companies specializing in custom built, billet aluminum wheels.
Budnik and Coddington were not at the show, Billet Specialties had no interest in what I wanted to do (build a 5 spoke wheel while maintaining the 6 bolt pattern), but Colorado Customs (coloradocustom.com) was willing to build it. They would do a computer rendition, then forward a photo for you to sign off on, to make sure you were OK with the final look. Their website has some detailed information on how to obtain the correct measurements.
There are a few wheels made with a 5 spoke design, and 6 lug fit. Best example, which unfortunately will not fit the SSR, is the Foose Lusso SUV wheel - talked to them at SEMA, but no interest in building a specialty set for the SSR - too limited a marketplace.
I have a friend locally who specializes in rebuilding custom wheels - he has no sympathy or patience with customers bringing in bent wheels that had 30 or 35 profile tires on them. The ultra low profiles do not provide any cushioning on pot hole impacts, and transfer the impact to the wheels. In order to maintain anywhere near the original rolling diameter with a 20/22 combination, you would need to run on super expensive rubber bands. I'd love to have that look, but it only makes sense on a garage or trailer queen - I want to drive mine, so it'll be new wheels, with the OEM tires.
The nice thing about custom billet wheels is getting the look the SSR should have had from the factory. The rear wheels are 2" wider, and all of that will be on the front lip, which really enhances the "hot rod" look - narrow fronts, wide rears. Too bad the factory wheels were not built that way. Instead of showing a wide lip on the rears, they chose to curve the spokes instead. The rear hubs are 1 1/2" deeper, but the spokes end up looking the same.