Being a LEO, I have been shot at and have shot back...
When SHTF, I can assure you you'll never feel the difference between a 5.5# or a 3.5# pull. I carried a 3.5# in my on and off duty Glock's for a long time and now I have grown a bit wiser.
The most important thing is training, and I don't mean a trip to the range. Practice dry-firing, it's free, and a GREAT tool. Practice drawing from your holster that you'll use dressing like you'd dress. Start slow speed will come with time.
3.5# triggers are fine, and if one trains enough I'm sure it's perfectly fine. However, I know first hand what goes through your head during a SHTF scenario.
I shoot from the "reset" on my Glock, this is how I've trained for a very long time so it's second nature to me. The upside to a 3.5# is a lighter trigger pull. The down side, regardless of what you do, it's going to get the trigger a little mushy and will soften the feel for the reset.
My personal guns are set up like this;
Olive NY trigger w/ spring removed
3.5# connector
This combination gives about a 5# to 6# pull but a VERY good crisp break and a VERY firm reset.
If I'm bullseye shooting, that set up isn't the best. The slightly heavier trigger isn't the greatest idea for "bullseye target shooting". However, in my opinion it is the best set up I've ever used for combat / self defense. I've tried every combination you could imagine in my guns, this works best for me. I'm not at all trying to sell you on this idea as it's just my opinion. I will be the first to admit, when I first tried this set up I HATED it. I told myself I'd try it exclusively for 500 rounds and then decide, I'm glad I did.
Any questions please feel free to ask.......