So honestly, with Caleb and Devin on the block, if the house as a whole wants to better their combined odds of winning, they'd vote Caleb out.  The guy is a competitor.  He's probably more of a physical threat than even Devin, AND he plays the social game.  He's a dangerous mix of social, physical, nice, and a little intimidating.  If they vote him out this week, everybody still hates Devin next week.  If they keep Caleb around, he'll gather a group of folks willing to ride his coat tails till the end, and then that group will fight it out.  Best choice for a longer term level playing field is to vote out Caleb this week, take your chances with Devin next week, and hope to get him out in the next 2 weeks.  Devin won't ever have the numbers to go with the brawn...Caleb might.
Oh, and totally agree 100% that Derrick is playing this season the best so far...under the radar, but in the game.