Don't waste money on extras if you're not going to use them. I bought a USP Compact Tactical not too long ago with the express interest of shooting it suppressed. I've already gotten the ball rolling on setting up an NFA trust. If you have no desire to spend the extra money on the $200 tax stamp, the waiting time for the ATF to process the paperwork and the cost of a good suppressor ($600+ easy), just buy the regular version without regret.
Adjustable sights are overrated, too, by the way. How many of you bother to ever readjust the sights for whatever reason once you have them zeroed-in?