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It's good to see the discussion include body position. The critical reference point is the BB. With older bikes the slack STA ended up putting your hips way behind the BB which is horrible for pedal power. The benefit of the steeper STA comes from moving the riders hips forward relative to the BB. Decreased angle at the hips (bent forward) _and_ hips closer to or ahead of the BB makes a huge difference in the amount of power a rider can generate. Of course being too far forward or forward for too long is a drawback as it puts more strain on the lower back and shoulders/wrists, so there's a happy medium that needs to be found. So for mtbs, STA is only one part though of the bigger equation of overall bike fit. IMO for the average rider who just climbs up and descends, a position that puts their hips slightly behind the BB and their upper body bent forward about 35° will offer the best combo of power and comfort for climbing. On flat road a more upright position where you sit and spin will be more comfortable but it will limit your power generation for hills, especially steeper ones. I think with mtbs there are more sacrifices that have to be made for comfort due to the nature of the type of riding the bikes are meant to do.
The key thing to look at in the pics is the positioning of AJ's hips in relation to the BB and the rear axle. On the Evil he's much further back and on the Geometron he's further forward in relation to those two points. You can notice the same observation on the Specialized which is why he says the G1 fits better.
Edit: as most descending around here involves the seat all the way down, I set my bikes up from the perspective of climbing efficiency and power and deal with a more awkward flat pedaling position as I spend next to no time in that scenario. The Switchgrade is a great idea that tackles the problem of seat angle. I also think there's a riser post out there that does this automatically as you raise/lower the seat.
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