I'm using snow studs - fewer studs for clear sections of road, and slightly more aggressive tread for off road sections, but I'm sure the marathon spikes will be fine.

I've never bothered changing to flats for winter riding - even when riding in on 23c slicks through 2" of mixed slush and ice. I have winter spd boots with toe studs.
The idea behind the spikes is that you don't get 'moments' where you need to tripod - be confident and plan your line well in advance! Take routes to avoid traffic where you can (not always possible, I have to ride through Bristol everyday).
Even on spds I can get my feet out plenty fast enough to catch a slide on non-spiked tyres. Thats if you have warning, if you hit black ice you'll be on the deck before you know anything about it, let alone chance to get your feet out to 'save you' - even if you could you'd just end up doing the splits.