The reload, cyclic and capacity upgrades all seem to be situationally viable on the ready rack (depending on how many shots you need to fire), while the capacity upgrade seems to be the best option for the magazine loader (with the reload upgrade failing to be relevant and the cyclic upgrade trying its hardest).
If you're going for sustained DPM, the magazine loader with the capacity upgrade is your best bet.
Of note is that the cyclic upgrade on the ready rack is the best option if you only want to fire 3 shots, after which you will want to use the capacity upgrade with either the ready rack (for 4, 5 or 7 shots) or magazine loader (for 6 or 8+ shots) with the cyclic upgrade on the magazine loader being the best option if you want to fire exactly 10 shots.
Edit: corrected the spreadsheet.
A combination of a capacity and cyclic upgrade for the magazine loader seems to give the best sustained RoF, but this can be changed to using a pair of capacity upgrades if you want a slightly different flavour of magazine loader.
The reload upgrades seem to be pretty useless (they focus on sustained DPM, and are outdone in this regard by the other upgrades) unless you really want to have a ready rack.
Using 2 cyclic upgrades is really only for memeing on people by dumping 2/3 shots into somebody in quick succession, at which point you will have a very low sustained DPM for the rest of the engagement.
