I use the OE 16s with a set of Pirelli winter/snow tyres on my Spider, although this year for the first time im not really planning on using it unless its a bright sunny day - so the summers will probably stay on.
If you are switching to winter tyres any time in October is a good bet - if the morning commute is done in temps around 7c or less its time to do the switch. Im expecting night time temps here of around 5c from mid to late October, so the winter tyres are going on my hack soon.
-1998 916 Spider 2.0TS Lusso-
H&S Corse stage 1.
CATCAMs stage 1 cams with Savali custom ECU remap.
305mm discs with 166 4-pot callipers.
Ragazzon exhaust mid section.
Biscione Racing 2x70mm rear section.
17" Zender Siena wheels with 3mm rear spacers.
etc etc etc!