Oh yea latex tubes are great! I also find them easier to change than butyl tubes as well. Though I have heard others have problems. Just beware using them with carbon clinchers, they have a lower melting point than butyl, so a heavy guy, on a hot day on a steep descent is something to be aware of.
5 watts per wheels seems pretty high to me though, the numbers I've seen are more like 5 for the whole system on the high end. Still a significant difference though. Some data here.