I would not use servo's in a run all day antweight. When we use servo's for drive in an antweight we run them much harder than they are really designed to be used but get away with it because they are only run for short periods. Running them continuously is asking for trouble.
That's a shame, that means I probably won't be able to make a run all day bot in the near future, as I don't have the money to buy new motors/speedos at the moment, I've just spent loads of money on my new ant.