I found the Neuvation method very interesting, they assume a static saddle to BB relationship:-
Bike GeometryThey class reach as BB to HT measured in the same way as you would measure effective top tube. Put another way a vertical line from the BB that bisects the effective TT line and use the measurement from there to HT rather than ST to HT.
So, if you measure that on a bike that fits you well then you can apply that measurement to other frames to see what size works. It's just a shame that all the little geometry charts don't include this. Say you had an ideal of 385mm reach and looking at their geometry chart. You could go with the any of the frames and just add/subtract the difference to your existing stem length. Obviously you'd be more likely to choose one of the closest matches, above or below, but it does give you an easy reference point for comparing frames.
Thought I'd share that, probably old hat to a lot of you, but I found it much easier to understand than other methods.