The hubs may be really heavy. I just went from no-name disc hubs to shimano xt disc hubs and noticed a big difference especially in the back. I've been told that cheap Bottom brackets can add alot of weight, I was forced to replace mine with an XT because I bent the axle. Going up to an XT cassette made a noticable difference as well. You might consider ditching your bar-ends if you're using a riser bar anyhow.