Just checked a couple of machines i have drawn.

For a really well designed machine capable of aluminum everyday/or even steel/ , without compromises and very tight Z and well thought gantry 500mm is the correct length. That having in mind 3kw spindle or even bigger as possibility. Lowering it to 460mm will compromise a couple of small things but nothing major if the intended spindle is 2.2kw and the machine gantry is no longer than 700-1000mm

if its for a big machine, longer than 1500mm, i would not do that compromise. Not that it will not work, just not to save money from this one