Wonder if this is due to the overclocking?
No, or at least it shouldn't be. As I said, I've only had the errors twice, and they were both when I had too low of signal (in house, 1 bar). Simply toggling it again I could proceed with no issue. This was back from when I first got my first elite back in July, all the way up to now - before overclocking, and after overclocking. The overheating seems to be a problem regardless of whether or not it is overclocked, simply because 3G is very power hungry and takes a lot of CPU power because 3G is fairly primitive. 4G actually would/should perform much better if we had it available.
Another factor in this is that 3G isn't actual 3G all of the time, as it goes all the way down to 1X without ever showing up, and oscillates between everything 3G and below frequently, which also attributes to the resource-eating, overheating, and battery draining. I only use 3G for Google Maps whenever I need it, and aside from the two times where I had almost no signal I've never had a problem - went over two hours many times without a reboot issue, though the phone did get very hot every time (no matter what other type of wireless/mobile network I use, such as wifi or bluetooth, and/or regardless of any game I throw at it, I cannot get the OE to overheat to an even remotely close temperature that it gets to when just using 3G after an hour or two).
tl;dr It's a 3G thing, and always will be because it is, after all, 3G. Use it sparringly (and I'm not sure there's a good enough reason I can think of, aside from commuting on a bus or train, where you would need 3G active all of the time outside of using something like Google Maps - but I'm sure someone has a good reason for it). Wifi is always preferable, both in speed and because it does not have the issues (which includes the overheating) 3G does, ever.