Bib short sizing.

Looking at some Stolen Goat Ibex Everyday bibs and / or some Rapha Core.  

In most bottom half gear I already own I'm in an XL or  XXL for thigh room.

I do not have a beer belly but do have larger thighs and "sitting facility".  

The Stolen Goat website says size by the larger of waist and hips in cm (100/112 respectively).  That puts me a couple of cm into the XXXL on hips but XXL on waist. 

On Rapha I'm potentially an XL but probably slightly comfier in an XXL  working off the larger measurement.  

I don't care about the label I just want the right size without sending back and forward. 

Do I trust the charts?  Any real world experience on sizing so the legs aren't tight to the point they creep down? 

Road riding holiday looming and woefully behind schedule on the kit buying.