These are the rims I just bought. They are 17" replicas of the 18" Mini GP rims.
Specs:17x7 42mm offset and 56.1 center bore.
They are aftermarkets but since they are "replicas" they have a single set of bolt holes and a 56.1 CB. No need for hub rings(I giggle every time I say hub ring, I'm not sure why) and stock Mini center caps will fit too. This will make customizing/changing/rechanging center caps(as my tastes change), down the road a lot easier.

Now I'm looking for tires. I'm planning to wait until I wear my 15" tires out first but I'm sure I'll get tired of that and just go for it. I was hoping to land a 17" tire diameter somewhere between the 23.96 of the 175/65x15 tires and the 24.26 of the 205/45x17 tires but that would be a 225/40x17 and I'm not sure those will really fit on my 17x7/42mm offset rims without rubbing or being squirrely. Has anyone tried that size? Erroring on the side of causion I've remained within the more common sizes below.
Some all season performance is acceptable but with the climate of this area it isn't necessary. A sporty feel and above average performance without the harshness of 17" runflats is preferred. I've narrowed it down to these four:
Hankook VENTUS V12 evo - only available in 205/45x17(most raved about in other Mini forums)
NITTO NEO GEN - 215/40x17(also raved about in other Mini forums)
General AltiMAX HP - 215/40/17(grand touring tire so less aggressive but folks still like them in the Mini forums)
GENERAL EXCLAIM UHP - 215/40x17(scored well in most reviews but not mentioned much in the other Mini forums)
I like the larger foot print of the 215/40x17 and is has the closest diameter to the stock 15" tires I have now. I'm leaning toward the Hankooks though, because of the comments in the forums, they have a wider sidewall than the 215's to protect the rims from bumps and potholes and the taller diameter will fill the wheel wells more. Who out there has what? What is you all's opinion?