OK - I was finally able to do a preliminary test with my cge-pro - but only of the slewing behavior and the ability to correct it, i.e. an indoor test with no sgp involved. This is the same as I did above with the evolution mount.
In this case I told the cge-pro to slew to 3:00:00 RA and 0 dec. - with the full telescope and imaging payload.
When I did this several times it consistently missed that target by -1.7s RA and +35" dec, with an occasional difference of 0.1s and 1". Again - this is just reading the handcontrol RA/Dec values after doing the slew - so there is no plate solve involved. The slew did not land exactly where it was told to land.
The error here amounts to 25.5" E/W and 35" N/S - for a total miss distance of 43".
I then made new slews that compensated for this fixed error - and told it to go to
RA 3:00:01.7 Dec -35"
On repeated slews it either went to exactly 0:0 or it missed the RA value by 0.1s or 1.5" - meaning a single compensation nailed the target repeatedly.
This is exactly the behavior I expected - and I observed similar behavior and improvement with the evolution mount - though not to this degree since the evo mount isn't at the same level of performance.
This doesn't mean the final centering accuracy with sgp will be 1.5" - but it does mean there is an inherent fixed miss due to the slew behavior alone that can itself be removed by compensating for it in the slew target - while a repeated sync/slew would never work.
When I have clear skies I will try the actual sgp implementation to test it for real under the skies and with plate solves.
Frank