one more thing that you may or may not be aware of: there are volumes of threads that you may want to peruse on the longevity of aluminum vs. steel. the long and short of it revolves round the fact that steel will only fail when there is a very large force applied, whereas aluminum will eventually fail due to accumulated stress fatigue. unless you happen to be a mechanical engineer, the evidence on both sides sounds convincing. the debate rages and there are people in both camps who are literally foaming at the mouth
after researching some of these threads, you may want to consider a steel bike for the more comfortable ride and for longevity. just a heads up on this if you plan on "occaionally" riding off-road for many years, and would like to still be riding it 10,15, or 20 years down the road.