The general fit is the same across the lasts but what makes a difference is the toes. The fit is all subjective based in how your toes are positioned and their size. If you have large toes or a big toe that sits farther out from the others, you most likely will feel like the tg73 or dg70 are too tight because they are aggressive in how the toes taper in so quickly.
If you have a large toe that goes towards the other toes or a small bunion starting, you probably will do better with the same size in all lasts because they won't put as much pressure on your big toe.
Long toes vs short toes compared to the heel to ball Length can make a difference as well. If your heel to ball length is longer than your overall foot length (I.e. UK 10 heel to ball vs UK 9.5 overall length) you probably will have less problems in the same sizes between lasts because your toes won't go up to the most tapered part of the toe boxes because you will choose the size based off of your longer measurement (in this case the UK 10).
if your overall length is longer than your heel to ball measurement (long toes) then you may need to consider changing sizes for the more tapered lasts due to the fact that your toes will go more into the tapered parts of the toe box.
Changing the width could also be a way to help this because the most important measurement is the heel to ball so your foot sits in place Better.
The other problem is how the toe fans out from the center line. Some have feet that grew inwards, some are neutral, and some grew outwards. The former is will fit all G&G lasts or all those crazy pointy lasts as asymmetrical lasts are all the rage nowadays. The middle will be a bit harder to fit but should squeeze in most w/o much problems. The latter one, which is most likely developed from unconstrained feet growth when young, will have trouble fitting in the more extreme asymmetrical lasts that biased towards the inside.