I built a spare rear wheel because I knew that if I would have issues with one thing at my starting weight on that bike it would be the rear wheel. I used a 32 spoke hub, an SRAM sealed hub, a BHS 500g rim (xc-279 if I recall right) and Sapim D-lite spokes. That wheel is 200g lighter than my stock wheel and maybe stronger to boot :-). My stock wheel I had some spokes which would back off and loosen up. The new wheel I built has been no touch since I started using it. Steady state lighter wheels are not faster, but accelerating they are, I do not really climb here where I live, but it would be nicer too. Different tires and tubes shaved a roughly equal amount of rotating weight off. I do not worry about getting sidelined if I have a rear wheel issue either :-). Plus now I have good tools to work on wheels. Point is that lighter wheels are not by default "weaker" wheels :-).