I would say the "standard" for 1/72 is 25mm base sizes since you can use 1/72 figures against 25mm figures (but not really against 15mm). Don't think there is enough 1/72 armies to have their own unique base sizes.
I currently have my 1/72 figures based 4 figures side by side on 4cm bases (since 4cm was the standard 25mm size used locally), but intend to rebase to 5cm bases to be consistent with a 25mm army I am just finishing.
A big advantage of 1/72 figures is you can pack them at the historic density. Troops deployed on about a 22" frontage (say 2 feet in action). If a man was say 5'6" then he deployed in a space equal to 33% of his height (or say 40% in practice). Converting to 1/72 figures, that means each figure should should a frontage of about 8mm-10mm. Try doing that with any other figure scale and see if the goblin-like figures can fit into the correct frontage!
That was why I used 4 figures on a 4cm base - it reflected the density of the men in reality pretty well.
3x2 figures spread across a 5cm base will look pretty sparse.
I will go for 4 figures in one rank on a 5cm x 2.5cm base with magnetic bases. For Lasalle I can use 2 of my bases together for a Lasalle base - but it does mean 48 figure Austrian battalions and 450 infantry in case they attack. Depressingly, I actually have them. Alternatively, I could use just the individual bases (not double depth) if I wanted a big army with up to 18 (smaller) battalions.
If you don't have as many figures, I would suggest using the 5cm base widths but with a smaller depth, and put 4-5 figures in one rank. It will look better. I have played a game with my figures on 2cm depths against the eneny on 4cm depths and did not notice any problems (although there will be times it could matter).
For cavalry I intend to use 3 cav per 5cm base.
Cam