For sure the quality spool if you're making power. The moser spool chops the shims in two because it has almost no landing shoulder for the shims, and the radius of the bearing corner cuts them. The strange, and the mark williams are the only 2 I've seen with enough.

I get as low as 1.16 60's in a 3400 pound car. Normal is 1.17 to 1.18 depending on track conditions. I had a moser spool, and stock caps, and every 10 runs or so the whole set up would be loose. From the pinion preload to side clearance. After the strange spool, and a williams cap it stays right where I put it, and the pattern doesn't crawl out as bad.

I also think the only gear company that gives a flip about accuracy with 60 pro gears is/was Motive gear. Richmond must make them on a wooden bench, as well as US gear. Just rolling the gear around you get different backlash readings. Motive was dead on at any position. Forget lapping the back of the gear with a stone too, it just gets worse. Motive gears, I'd take out of the box, make a couple passes with a stone, and they'd clean up instantly.

The pro gears bend, and take a set anyway, so I guess it doesn't matter, but it's annoying during set up, playing pick a spot.