Why not 555 or 666 GB?
There are no "best practice with numbers". The only best practice for choosing LUN size is:
1) leave 20% space free
2) give LUN capable to handle VM IO load. Doesn't matter, 2TB, 144GB or even multiple LUN 64TB datastore.
MCSA, MCTS, VCP, VMware vExpert '2009
You can find different post about this "problem"...
It depends on:
Storage best practice
VM number, size and type of I/O
Max LUN size (less than 2 TB - 512B)
Max VM and I/O per LUN
Usually a value between 400-800GB could be reasonable.