Well, I don't know about bending my knees wearing me out out faster, since I used to play 8-10 hour sets twice a week and felt fine afterwards. With this new stance I'm done like dinner after 3 hours.
I find the opposite is true about weight shift for me, since I'm a heavy guy. When I shift forward, my front leg starts getting tired really fast and my lower back screams. When I shift my weight back some and bend my knees, it takes the weight from my lower back and spreads it out more equally.
The way I look at it, my leg muscles are strong and designed to bear my weight and then some. My lower back is strong when standing straight up, but when I bend over, it's stressing those muscles.
I really want to find a way to center my cue under my chin naturally using my old stance, but I just can't seem to make that happen.