The reach to the bar tops is important so you can get a good pull on it while seated. Get back in the saddle, drop your elbows, and keep the bike from shooting out from under you by pulling on the bar tops. If the bars are too close, this feels really awkward. Too far away actually feels pretty nice in this position, but ruins every other part of your fit.

I haven't fully quantified it yet, but I've got another climbing position for moderately steep stuff (10% or so) where I can sit up really high, roll my hips forward a bit, and it suddenly feels like I'm using completely fresh muscles all of a sudden. I get to do this for about 1 minute, and then it's over, back to being tired again.

Frame stiffness is a personal preference thing.