I can tell the difference between Octalink Hollowtech cranks compared to Deore HT2 (open C section arms) and LX and XT HT2 set ups but that is understandable.
Could I tell the difference between HT Octalink and non-HT ones? I doubt it as the difference is very slight (mainly weight is the benefit) and there are plenty of flex in the load path from my legs to the bike frame.
Which brings me back to HTII cranks – you foot, sock, your shoe bindings, shoe sole, SPD/pedal pin interface, pedal axle etc are all sources of flex. Obviously the crank is the longest length so any give will have a larger effect but as the cheaper non-HT2 cranks are slightly heavier I suspect the stiffness in simple directions is quite close, they are also probably a bit tougher than thinner walled ones. The closed section cranks should have an advantage in torsional stiffness but is that important when you compare it to the other sources of flex in the load path?
The steel pedal inserts – do they actually benefit stiffness or are they there to be tougher? A DH/freeride set of cranks are likely to experience more shock loads and the tougher thread material and increased area for bearing load into the aluminium arm are beneficial. It actually adds an extra interface between the insert and the arm which is a potential weakness.
Stiffer axle – again it’s probably more there for the shock loading from jumps etc to stop it deforming when you consider all the flex that is in the frame to BB cup, BB cup to bearing etc.
I’m not saying there isn’t a difference in stiffness but I’d like to see the results of a verified model or some real load testing as I suspect a majority of the effect is placebo – you know there is a difference so its playing on your mind. Can you tell the difference between the drive side and non-drive side crank on a HTII because a pressed fitting is a lot different to the clamped one.