I came across this while researching Snatch Blocks, i found it very interesting at just how easy you could unkowingly exceed a Snatch Blocks "safe working load", all because you used a Snatch Block in the first place !
Snatch Blocks
It also appears (from other research) that the larger pulley size Snatch Blocks are better for both Cable and Rope type winches (well, for the rope/cable not really the winch)
One thing i have discovered, is most Snatch Blocks available at common auto stores, have quite small pulley wheels ,and also quite a large gap at one end between the wheel and the housing when its all closed (as you would use it), i can see this gap becoming a potential issue if you use rope instead of cable, as a winch rope under tension could squeeze between the gap (steel cable would not be such a issue as it would not compress)
I ended up with a 8 tonne Maxi Trac 125mm Snatch Block, it has a smaller gap and a larger pulley than all the others i could find in the flesh.