I run Ubuntu on a X1 Extreme Gen 2 for a while now, no problems whatsoever. The discrete nVidia GPU is as power hungry, and running as hot during gaming, as it did under Windows (so nether a big surprise nor a real problem, anyone remember how harsh Battletech was on GPUs initially?). Battery live, depending on use (and excluding gaming) is around 4 hours (didn't have less then 3+).

The heat issue is mitigated somewhat by putting the machine on some kind of stand to have air pass underneath it. That being said, even under Windows the machine went to sleep just fine, also woke up again. If anything, that works better now under Linux.