Re: 17" Vs 18" wheels
Ditto, skip the NAV and go with 18's or 19's. The 18's are a good handling compromise and are less noisy, lighter, and not as vulnerable as the 19's. Love my heated/cooled seats here in Houston. You can also save some bucks and weight by getting the mechanical (non-motor driven) seats as well.
2009 2.9L Guards Red Cayman: 18" S wheels + SC + PSM + PDK. Added: FVD exhaust,
GIAC DME code, Evoms V-Flow filter with partial desnork, SS brake lines, H&R rear bar
with Tarett links, matte black side vents and front grill mesh, and 3M 50% window tint.