The beast that spawned them:
Top with Ashford Jumbo flyer used at speeds of 1,600 to 1,000 rpm ( the two skeins of cable were done as one big bobbin full.) And, below is the AA #0 (Competition) flier used at speeds of 2,400 to 4,200 rpm.
The Jumbo flyer has 4 drive whorls. One would expect that the little 1.75" whorl to give more speed than the 2.75" whorl, but there is so much slippage that it does not. Spinning wheel drive belts slip a great deal. Still with the accelerator, and using the larger whorls, plying/cabling goes about 40% faster than is possible just using the Jumbo Flyer (with a Alden Amos Bumpless drive band to minimize drive band slippage.) With the stock Ashford drive band, I never got the Jumbo Flyer over ~450 rpm. When plying up gansey yarn at 9 tpi, that is slow!!!!!!!!!
That bobbin of the AA#0 will hold about 12 grams (0.3 oz. ) of yarn. If one is spinning 40s, that is a neat 560 yards. Amazing how that works out. With the accelerator, I run it at about the same speed as I did without the accelerator, but I can treadle much slower. This is set up with the flier/bobbin mounted with ball bearings. A test shows that it will go just as fast using bronze bearings (with more frequent lubrication.)
Why not just go to an e-spinner? While I do not "count", spinning is very rhythmic, and my cadence sets the beat for everything else. It took a couple of days to get used to the accelerator, because now my hands have to go twice as fast relative to the cadence. With an e-spinner, there is no cadence so my hands do not know how fast to move.