I would say that whatever pleases you and makes you feel comfortable should be what you wear.

My dress sporran sounds very similar to yours - and I personally like the look of the white fur and silver. It sets off the white shirt (or when I used to wear a Montross the white jabot and cuffs) and silver metal (buttons, buckle, kilt pin, etc).

I've seen the Saltire and while I would say it is entirely appropriate for a dress sporran, I don't much care for it myself. But, like I said, you need to wear what you like and feel comfortable with, so if you like the Saltire, go for it.