Hi Vincent,
I'm using 7.2 with 4.6.3, not 7.3, so I cannot describe how difficult it would be to use it. However, if you check the bug tracker[1], you will see that there are some bugs for openacs using 7.3 that have been fixed for Openacs5.0 (but not 4.6.3).
It seems that 7.3 is in the openacs 5.0 development wave, whereas 7.2 is used more with a matured 4.6.3 revision cycle. (Corrections by the experts appreciated.)
cheers,
Torben