There seem to be other anecdotal reports of this sort of behaviour although the exact details are not totally clear to me. E.g. some people seem to experience that if the phone goes to sleep with 3G rather than 2G enabled then it can crash. I have had a few crashes which may be due to transitions between Wifi/2G/3G but I don't know for sure. I'm using CM10 and I believe that my last stock update (and hence RIL - Radio Interface Layer) was B936 Vodafone Ireland. Some people have claimed that they see improvements if they flash the B926 RIL but again the exact process for doing this safely is not clear to me - I think you may have to do a downgrade to GB, then flash the full B926 update and then go to another ROM while retaining the B926 RIL.
I am probably confusing things more than helping here!
I use 3G/Wifi all the time and I never had reboots but sometimes I see network signal being lost for a couple of seconds when using 3G.
Btw, about the swiftkey crashes Daz, I'm now using the SK flow beta and it's running smoothly.