OK thanks for the replies. I suppose I need to choose a stackup, use default values for FR4, then let the PCB house tweak the geometry based on fab notes/instructions.
@daqq - yes I do plan to make the runs short, however on this device (Sierra Wireless WP7607) there are 3 antennas for LTE (main) LTE (diversity) and GNSS. Two are on the bottom of the device but one is on the side meaning the trace has to go "around the corner". Even so, max trace length is only about 30mm or so (hopefully, I've not started the board layout yet).