Originally Posted by
SoSmellyAir
Now I get what you were getting at: If in between sizes, pick the larger one to get more stack but use the next shorter version of the stem to maintain approximately the same reach.
Do note that some carbon fiber seatposts, e.g., Cannondale Save, Canyon VCLS 2.0, require a certain length of exposed seatpost to maximize their dampening effects. Picking the larger frame reduces this effect.
Yeah, I tend to go more off stack height than reach when looking at frame sizing. If I was on the fence between two sizes I would tend to size up for a longer wheelbase and higher stack for endurance riding. A lot of racers do the opposite and size down to get lower. Stem length is pretty easy to compensate for within reason. It's a good point about seatpost extension vs comfort. Definitely something to bear in mind if sizing up, but wouldn't be my primary concern as long as the post wasn't slammed right down - which would indicate a frame way too big anyway on a modern bike.