That is a tough question. Tstark was correct in his answer. However, you must design your layout to accommodate your future plan. It is all on you. MTH double stacks are more than 6 inches tall.
The issue with making all your clearances 7 inches is that it may necessitate steeper grades and will it be necessary to plan such clearance if your tallest piece is 5 inches?
I do think that generally the best piece of advice is as Tstark wrote. Ultimately, it is your decision.