From what I have seen, usually you put steep slopes for the sub. Helps to create "invisible" bass that you can't detect, so crossover fairly low, no higher than 65-70 IMO. Also steep slopes for the lower high pass of the mids, 18db or higher. For the upper mid lowpass use a less steep slope to blend to the tweeter 12b or so, then for the tweet high pass use a steep one for protection...
Hope this helps...
One more thing, for the mid high pass it all depends on if your doors are deadened and how low you cross them over. You dont need a steep slope if your cross at 80hz or higher, but I would advice using a steep on if you cross lower, like at 60...