Weight Weenies

Seems like only stems I can find have 40mm steered tube clamp stack.

Other specs :
6 deg
100-110 mm
31.6

Preferably aluminum

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Or, is there any compression plug that adds on extra 5mm or so of clamping area above the steered tube?

In hesitant to go with 0 degree, or riser stem because they look goofy as fudge.

For what it's worth: Deda makes the aluminium Superzero stems - these have 36mm stack height which could be close enough for your purpose, but they are 8° (doesn't make a huge difference with 100/100mm length) and nominal 31.7mm bar diameter.

Deda Superleggera RS
34mm stack (true measure height)
-8 degree

lets see if i have my basic math correct.
stem length, and angle being equal, the difference in bar-clamp center would be 2.5mm between a 35mm stack and a 40mm stack (when measured from the base of the steerer tube clamp)?

looks like i'll be ok

There're a couple of online calculators in this thread https://weightweenies.starbike.com/foru ... 3&t=154459

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Mind that going from a 6° stem (your current situation) to an 8° stem (Deda) will also lower your bars by a few mm. Nothing disastrous imo.