Brant - excellent summary. You're right in every respect. If/when I get the R5 I will probably opt for the battery grip, as much for the vertical shooting convenience as for the extra power. It should pretty much eliminate the frame rate reduction due to battery drainage in most daily use.
Having options like the R5 and the 1DX3 is like being able to choose between a Ferrari and a Lamborghini. You can't really be critical of either. For me I'm going to stick with the 1DX3 at least until a R5 Mark II comes out (in four years' time, I would guess). I think we're going to see even bigger things to come in terms of frame rate and hopefully the same AF-ON trackpad that is on the 1DX3.