Would you mind elaborating on this please?
I'm 6'1" with a 32/33 inseam. Considering a Medium 2015 Shiv Expert. What are your concerns with the medium? Have you raced in an aero position extensively?
I've spent lots of time in an aero position. Below is an image of a "slack" position I was experimenting with earlier this year for long course on my Speed Concept (ignore the helmet, didn't have the tilt set up right with the straps). IIRC, my pad stack/reach there was 645/545ish (measured to the center of the pad... that's how I measure). The reach on a medium Shiv is 405 and on a large it's 425. So, to hit that reach on a medium I'd need a 140mm stem which is waayyyy too long (too much weight out front). On a size large Shiv it's more like 120mm which is still on the long side but acceptable.