I think many of you are giving Nails too much credit. He hasn't really shown much, and in my opiniion would likely be the first to be on the cut list out of the offensive lineman. Many of you also aren't giving Andrew and Cesario much of a chance, in my opinion, just because they aren't "names" you can recognize. But, both of them have talent, and more importantly are YOUNG and VERSATILE.
If it comes down to a close call between one of the younger guys and Nails, I think the youngster would win out 9 times out of 10, just because there is more of a chance of them developing into their potential. Nails had his shots and hasn't done much with them, it wouldn't make sense to keep him around if that is the case.
Also, along the O-line your backup guard usually fills BOTH backup spots. Right AND LEFT, so even if they are currently competing at, say, RG... that doesn't mean you automatically have to pencil in a guy from the LG spot. Things are still early and its will probably be a while before we see how the O-line shakes out.
My pick for the likely depth chart:
POS - Starter (Backups)
LT - Smith (Spriggs)
LG - Dixon (Perry, Andrew)
C - Ruddy (McKinney,Andrew)
RG - Searcy (Perry)
RT - Wade (Cesario)
... although, it could look like this (and might be prefferred):
LT - Dixon (Smith OR Spriggs)
LG - Perry (Nails)
C - Ruddy (McKinney,Andrew)
RG - Searcy (Andrew)
RT - Wade (Cesario)