That last painting is one of Morgan Weistlings, check out the awesome demos he has on his site - can't link to it as it's ... I dunno, not link friendly. That painting is the first in gallery one though.
On these studies, I would really recommend breaking things down into smaller parts so you can really tackle them, what is it you want to focus on most? If it's accuracy then I'd try some line drawings, if it's form and shapes and perhaps technique then I'd do value studies, if it's color - I'd do something else... hehe. It's just not as productive if you have to wrestle with learning everything at once you know?
Also; CA Gift Exchanggggge!