Based on my own experience with standing desks and high-end office chairs (the most recent being a Herman Miller Embody, which I ended up selling), I've concluded that I need an office setup that allows me to move throughout the day and not just stand or sit nearly motionless for most of the day.
After trying out all the chairs at my local office furniture stores (yet again) and enjoying a Swopper stool that one of the stores had in their showroom, I'm now planning to order a Swopper Air. The Swopper is the most comfortable active seating solution that I've tried (but I haven't spent hours sitting on it yet).
I hope the Swopper Air works out for me. If not, I'll finally pull the trigger on a LifeSpan TR5000-DT3 treadmill for my standing desk.