Assuming all are healthy at the same time, and assuming we do re-sign Baby and Sheed's deal is done, I see:
KG: 30
Perk: 30
Sheed: 26
Davis/misc4/5: 10 min/injury insurance.
Here's why: 96 minutes total for the 4/5. Wallace is completely capable of playing either forward or center on either end. KG averaged 31 minutes a game last year, i figure a little less. Perkins averaged about 30 last year, and has actually increased his playing time each year and is only 24, so he could play more, but that's a conservative estimate. Wallace was at 32 last year, so a slight downtick to keep him fresh is ok. then whatever's left for Davis, since he's clearly the least valuable of the four. Or, he could step in if there's an injury. however, this may be why, if memphis is still interested in Davis, you could swing a sign and trade of Davis for Warrick (maybe possible since warrick hasn't seemed to garner as much interest, and could sign for about 2.5 per year or so and memphis is under the cap) because warrick can play the 3 or the 4 and is super athletic.