Thanks for the feedback guys !
I just got a PM from davek (I ask him for his thoughts) he shared this with me...
The bacterial activity taking place in a deep sand bed is mostly anaerobic (without oxygen). This is opposite what happens with live rock, which is aerobic (with oxygen). So you should not decrease the amount of live rock on the basis of sand bed depth.
I don't think I would be making a mistake if I went with 2 1/2" Tom & if I get borrowing fish like you did they could re-arrange it - that depth works for me now.
I got to do some more thinking & homework here... was nice to learn I don't need to add less LR, just because one goes with a DSB... now I am thinking less might be better... hmmmmm
All advise... appericated... I don't think there a real wrong answer... my 2 1/2" sand bed I have now works... just thinking, now that I have a chance to start over... is there a better way