PPD40 is not at all more accurate or even controllable than the PPSh in my opinion.
Sure the PPSh41 has a more forceful vertical recoil than the PPD40, but in my experience (and this applied to the mod too) it has much more horizontal recoil. By that I mean that the PPD40 seems to fly wildly off to one side or another more than any other automatic in the game. With the exception of rested fire (where all the automatics are deadly) I can fire much more accurate bursts out of the PPSh41 than I can with the PPD40 from any position, standing, crouched or prone.
I rate the Russian SMG's this way;
1. PPSh41: High capacity, high rate of fire, suprisingly good accuracy when used correctly. Excellent from the hip up close with the trigger down and good for a little distance when fired in bursts. Looks mean, sounds terrifying, an utter classic of the era.
2. PPS43: good rate of fire, good accuracy, easily controllable, downright exceptional from the hip whether up close or at a little distance, only handicapped by it's small magazine size.
3 PPD40: High capacity, good rate of fire, shithouse sights, only decent accuracy. About the same from the hip as the PPSh41, but lacking that little extra bit of grunt in the firing rate. It really is pointless to even bother using this gun when you have the option of the PPSh41.
Seriously in the realm of SMG's the PPSh41 is ruler of the roost.