How did you get it down to 4.5 lbs? I did the trigger job with the pig tail spring and polished the heck out of the trigger components and i'm at 8-9lbs. I have heard some not so great things about the Wolff spring. Its great for the first 1,000 or so round and then there are alot of FTF's. I have about 18,000 rounds thru mine already with out any problems at all and am fine with the trigger as far as putting a bullet where i want it to go. I am just a tinkerer and like to mess with stuff.
I really like my sigma out of all the pistols i have, it gets the most attn.