I do not know about Sun, but a lot of rims vary from batch to batch and
are not always true to the advertised ERD. I know I've personally had
this experience with ALEX rims, and I think Mr Bunny also mentioned it
once upon a time.
Do what you want, but were it me, I'd wait for the rims to arrive and
measure the ERD myself. This is the calculator I use
wheelpro.co.uk