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Without the roll mark and match trigger you are looking at an SD model. It’s essentially a USP with a threaded barrel.
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This.
That also effects the price a little bit. That is why it is under a grand.
From what I read online, the SD model is just a standard USP with a extended/threaded barrel and taller sights.
The tactical (the slide says tactical) has the O-ring barrel and match trigger, and taller adjustable sights.
Now if the extra few hundred dollars is worth it to you for the slide marking, barrel and trigger is up to you.
I venture a guess and most regular shooters would not really be able to tell much of a difference (accuracy and performance) between the two. But some professional/match shooters might be able to. The trigger would probably be the most noticeable difference in feel.
With all that said, I just bought a tactical a couple weeks ago and love it! I chose the tactical over the cheaper SD specifically for the roll mark, o-ring barrel, and trigger.