Congrats on your new SHO! Best car I ever owned (miss it already). I had the performance package on my 2010 SHO and used Michelin Ice snow tires on 17" rims for the winter. I replaced the compressor with one of the mounted snow tires for my spare (fit perfect circumference wise, but was taller than the spare well was deep). I think getting the performance package and then getting rid of the performance tires that came with it is was what the previous poster was getting at. IMHO having the Eagle GTs for the summer and having snow tires/rims for the winter is a better solution than buying year round tires. Discount tire will swap them out each season for free if you but them there. I spent $1,100 for the tires and nice 5-star black powder coated machine lip 17" rims (smallest diameter that will fit with no clearance issues). It solved my no spare problem too.
Im doing the same thing. Dedicated snow tires with 18" rims for about $1,000. Snow tires for the oem 20" wheels were almost $1,200.