Concerning the T. C. of the 3458A, w/ and w/o ACAL, I wrote a comprehensive article here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg5230803/#msg5230803The 3458A will practically not drift, if not powered, therefore, it might still read very accurate.
The 10V cardinal point checks the 11V range of the 5440A most accurately, as this value is used for its basic calibration as well.
As said, the other ranges, 22V, 250V and 1000V, are calibrated once in the factory, and practically never need a new external calibration any more. The internal calibration will always reproduce the original gain factors.
Therefore, to check these 3 ranges of the 5440A, you need to measure 13 and 20V in the 100V range of the 3458A, 100 and 250V in its 1kV range, and about 276V and maybe 1kV for the highest range.
I wrote a longer article about the Fluke 752A precision divider where I also analyzed the different pitfalls of the 3458A, in conjunction with the 5442A:
https://www.eevblog.com/forum/metrology/influence-of-switch-resistance-in-hamon-dividers/msg4221751/#msg4221751E.g. those 13, 20 and 100V measurements are quite delicate, as ANY DMM has problems with E. M. F. voltages in this 100V range, due to the usual 100:1 divider. You need to make one careful null reading of the 3458A, 100V range, and subtract that value afterwards. Always use appropriate statistics on the 3458A, as described elsewhere.
Similarily, you need this procedure for precise calibration of 200mV and 2V range.
These about 276V will set 5440A to its 1kV range, but can be measured by the 3458A w/o it's mediocre heating /power effect at 1kV, which might be up to 12ppm additional shift.
I recommend again, to not do any external calibration on the 5440A, as it seems to be spot on within 1ppm
Frank