Im assuming you plan on going below 16" and want it attached to bring it up to 16"?
Personally I would just get the suppressor now, SBR the gun later, and be able to use the suppressor for other things in the meantime. Look at it this way, you spend the extra $200, but if you want to suppress something else you will have to spend $200 on a new stamp, plus the cost of the new suppressor.
I guess the third scenario would be if a permanently attached has better performance, but if you are going that route, why not go for an integral?