Personally, I find it impossible to study more than 8 hours a day over any period that is longer than a few weeks. When there are no lectures, I usually do about 6 hours (e.g. doing research [theoretical] or preparing for an exam). My habit is to go to university for about 8 or 9 hours a day and then use about 2-3 hours of that time to take some breaks.
Numbers in the region of 10hours+ sound really unhealthy to me, even if it is lab work. And I wouldn't believe any theoretician who claims doing more than 8 hours of productive desk work (should be comparable to regular studying). Anyway, most students I know do considerably less (even if they won't admit it)
Well, if you want to work more, I think the best way is to work e.g. 6 hours every day. 42 hours of good work (no distractions, no hang-over etc.) should be enough to get the most out of your potential.