Actually I just received a note back from Kervin at Rotor, he said that he just measured one of each and the 3D and 3D+ are supposed to be identical but in fact are slightly different:
3D: 145mm width at the pedals (Qfactor) and 135mm width at the axle
3D+: 151mm width at the pedals (Qfactor) and 141mm width at the axle
So the Shimano Octalink 105 setup is 145mm Qfactor and 130mm at the axle, for 7.5mm of ankle clearance on each side. The Rotor has 5mm of ankle clearance per side, which will probably be enough for me. But neither of them are the same as the nominal 147mm Qfactor that has been thrown around...I'm not sure if that will matter for me or not. I'll probably take my chances with the 3D+ SRM and just hope it all works out!