Depends how much you and your kart weigh. and how much vibration you can stand. Those 250 2-strokes vibrate quite a lot.
Everyone I've talked to with an off-road buggy with a 2-stroke says that it is absolutely AWESOME once you hit the power band, and if you want you can just spin the wheels the whole time. They do, however, bog down a bit at low revs as you say.
If the kart is light enough then it wont matter because you can just spin the wheels but if it's heavy then I would go for a 4-stroke.