First off, welcome to the Cafe.
1st round, 6th pick should still get you a good RB. And, just to get this clear, if you want to win championships you have got make the RBs the core of your team. I've tried every which way over the years and the results are the same, teams with good RBs win.
So, who might that be? If you're in an experienced league, you'll be left with McCoy, McFadden, Turner caliber. All great #1 RBs. If you are lucky and have a rookie drafting, you might see a QB or WR go ahead of you and land Charles or Rice even. Regardless, get a solid #1RB on your squad.
2nd round, gotta go on the hunt for a second RB. Don't get tempted to grab a WR or (heaven forbid) a QB yet. Sitting where you are, probably can nail down a Moreno, Hillis, Green-Ellis quality back. Great for your #2 RB.
3rd round, now for the #1 WR. There should still be a few out there unless you're drafting with knuckleheads who all want names over quality. When I mocked it this morning, I still found Wayne, Bowe or Marshall on the board in the 3rd.
And so it goes... my league plays with a WR/RB flex so I make round 4 my decision round -- best available of either cat.
I actually have been waiting until 8th and 9th rounds for QBs over the last few seasons and have done fine. In today's mock, I got Schaub or Sanchez in the 9th.
Keep doing the mock drafts. Keep playing with ideas. But in the end, you cannot go wrong thinking RB first.