Consensus on microstrip trace impedance calculations?
I ran the calculation for you in Cadence SigXplorer (my favorite tool for this and a lot more):



This is a 10.25mil wide trace (sorry units on the image are in metric) to give 50R pretty closely.

Always use a 2D field solver for this (as you noticed, formulas are not enough). 

Be aware that the SMA footprint may not be a smooth 50R without some great care as well. For this you can often get help from the connector manufacturer if you send them your stackup (and is deemed a worthy customer :-).

Disclaimer: I provide training in signal integrity often using tools kindly provided by Cadence. Other than that, I am not affiliated. Other tools can do the same thing. The only free one I have tried is called TNT.