Re: FNP ?
FNP45 tactical is based on the FNP45 USG with the addition of the milled slide, taller "suppressor sights", and threaded barrel as you noted. The USG models have a manual "thumb" safety and decocker while the regular FNP45s just have the decocker. I have a USG, its been a great shooter for me.
Edit: What I said above was true at the time I purchased. Later-model regualr FNP45s may have had the manual safety-decocker that only came on the USGs when I bought mine...I'm unable to confirm either way...