I am still running a 135 Chris King rear hub with the 10mm bolts on each side. I use a long handle 8mm allen to tighten them down. The bearings run directly on the one piece axle. I went so far as to make a set of dropouts so I could keep running it with my current frame (Banshee). I think it's the stiffest setup I have, other than maybe the 14mm threaded one piece steel axle on the rear BMX hubs. I do swap it out for a 10mm thru axle wheel for light duty if I don't want to carry the 8mm allen.
I torque the Kabolt 15mm axle on the fork I use for DJ to 17 nm. If you look at the Fox 15mm QR axle, it actually has a 5mm rod that stretches like a classic QR.
For 20mm axles I'm a fan of designs with a thru axle like the CK (one piece axle) or OS DT 240 (end caps thread onto the axle). A lot of them have the inside bearing races running directly on the fork axle, depending on the fork design the bearings can spin the races on the axle or rattle around, especially with variation in axle diameter.