Is there any real world difference between the two? why do they offer different size face plates, does the non-44 version cause bars to slip or is it not stiff enough?

150lb rider here.

It would be great to know is there is any noticable stiffness between the two from someone who has used both. 2 off standard version has no slippage issues for me.

I posted your query in the Ritchey sub forum over at RBR. Ritchey Dave is sure to provide a good answer for you.

http://forums.roadbikereview.com/ritche ... ost3804130" onclick="window.open(this.href);return false;

And here's the answer:

"Good question. The 4-Axis 44 differs from our standard 4-Axis stem in stiffness and weight. It has a larger, more squared, body to increase the stiffness. This stiffness is at the expense of about 10 grams compared to the standard 4-Axis, but sprinters, track racers, and larger riders have found it worth it. Climbers and "weight weenies", however, have preferred the 4-Axis for the more obvious emphasis on weight. The 44s larger faceplate is a result of the larger body, rather than to combat bar slipping, however it does add to a larger contact patch for the handlebars, which does reduce the possibility of slipping. For a maximum stiffness to weight ratio our new C260 stem has surpassed both our 4-Axis and 4-Axis 44 in all departments. Hope this answers your question.
__________________
Dave Law
Ritchey Design Representative "