You have to admire Gilchrist. Off the field also he seems like a nice bloke. I know Wasim Akram said he didn't like walkers for that very reason Twizzle, and also the reason they might not go in a crunch situation. Gillie did go in one in Africa so you'd have to back him.
On Bevan, he does look out of knick, but his record speaks for itself. I hear he has a groin injury which would take away all those short single options of his.
Martyn on the other hand is just having one of those runs. I think he's an excellent batsmen, just having a streak you just can't get out of. Sometimes the best thing is to take time out and re-evaluate. Craig McMillan was dropped from the Black Caps after a similar run after being probably our top test batsmen, he came back and thumped truckloads of runs in a test series in India - I'd apply the same thing to Martyn, give him a break out of the side and see how he comes back.