Hubs are just as critical as anything in a wheel's practicality and performance. I have had a few different brands and types and while a cup/cone full compliment bearing can be a low-drag design if greased and maintained, the short maintenance spans(in XC trail duty as low as monthly) were really annoying. Now I only use sealed cartridge(which I regrease with my own) and I only have to check the grease yearly(regreasing every 3-4). For someone to use everyday, any reduction in maintenance needs is huge. A little more cost in the beginning to invest in a lot less shop time.

As far as speed goes, I did notice a small increase in speed from the Sun Mammoth DH rims to Mavic TXC3.1 rims. The mavics seem less influenced by cross winds and go up hills easier, but the DH are a confidence boost when playing around.