Well, as you pointed out you have two choices.
A 6217 would offer a different look and therefore perhaps more variety to the collection than adding a 6306. The 6306 however fits the same theme in terms of case shape. Either way, both are winners. And both are likely continuing to increase in price alt...
I agree with the 6306
The 6306 is the more reachable goal. The 62Mas prices are really getting out of hand.