My 83 NA has Yokohama AVE ES 100's - they're hard tires, and it seriously sucks in the snow or even simply wet pavement. I tried snow one time and got stuck pulling out of my garage in maybe 2" of snow.
My 86 951 has Michelin Pilot Sport M/S and it does great in all weather. The Michelin's are a lot softer tire and are much more grippy than the Yokos. I've run it in 2-3" of snow and on ice with no real problems.
Both cars are daily drivers (I drive the NA M-W and the 951 Th-Fr).
Here's a picture of my son's 951 - which he drove to work today in the snow. A heavily modded 951 with better than 300 HP and it still did okay. He has the same Michelin's as I do. They really are great tires.
Lindsey MBC
3Bar FPR
951Max Chips
Lindsey 3" exhaust (no cat, no muffler - just a resonator)
Open Tial 38mm wastegate
LR Super 65 turbo
LR Stage 2 MAF
75# injectors, 17 psi
Innovate LC-1 Wideband O2 sensor and digital AFM gauge
Koni adjustable struts with adjustable ride height with 425# springs and solid strut mounts
Koni adjustable shocks with 550 # Rear Coil-overs (torsion bar delete)
KEP Stage 2 clutch and pressure plate
Lowered about 1"