Peter -

yes, deep cycle's can be used for winching/starting applications without harm. However, all things being equal, a deep cycle isn't going to give you as many amps... though it will sustain those amps much longer and recover from a deeper discharge. As long as you pick a deep cycle that can provide the current you need, you are fine to use one in a starting application... whereas using a starting battery in an application for a deep cycle will most definitely kill it fast.

the marine batteries you are talking about are what i was referring to above as a "hybrid" between a starting battery and a true deep cycle. they can't be discharged quiet as far as a true deep cycle, but provide you with the high CA you need for winching.

when looking at batteries, its all about cycle (discharge/charge) vs. life (how far you discharge) and picking the appropriately constructed battery for your application. As with anything, its all a trade-off

-Rob