Tongue weight on a TT should be between 10 & 15% of the TT weight, so 645lb tongue weight with a GVWR of 5143 is probably about right.
I had a wd hitch with a friction anti-sway control on my old TT. Had alot of sway, never too bad though, and felt the tug as semis went by.
I had the Equil-i-zer installed on my new TT and have only pulled the new TT about 150 miles but I can tell a real difference. Hardly any sway and I don't get "sucked" over by passing semis.
May be a few more bucks but worth it. JMHO