1911 trigger pull has very little to do with springs and very much to do with geometry. Here's a summary:
The hammer hooks must be an absolutely square 90 degrees and they must be parallel to the hammer pin. Any variance will result in either trigger creep or a gritty trigger (not square) or worse yet, a partially engaged hammer if the hooks aren't straight. Additionally, the hooks should nominally be .020" high. some prefer to go down to .018; I don't think it's necessary. My hooks are exactly .020 and I have a clean, crisp trigger pull in the neighborhood of 3.5 pounds.
The sear nose should actually have two separate surfaces. The primary angle should match up exactly with the hammer hooks when placed in the gun. This means you can't just purchase a "drop-in" hammer and sear and expect them to fit perfectly. If the geometry is off even a little bit, the trigger pull suffers. Sear-to-hammer engagement must be checked on the gun itself. I have a set of pins (drill rod would work just fine) that mount the hammer and sear to the outside of the frame, and a 10x loupe that allow me to check the work. A swipe of Dykem or even a Sharpie marker across the hammer sear nose will show how the engagement surfaces mate.
The secondary surface of the sear nose should be to the inside of the hammer hook, and should be cut such that the sear engages the hooks fully but that once the nose lets off there's no sharp edge to hang up on. This will facilitate the "break" of the trigger when depressed. It is important to leave about .020", or roughly 2/3, of the sear nose at the primary angle to ensure a safe amount of engagement. For those playing along at home, make sure you stone AWAY from the primary angle so as not to place a "hair" of metal at the junction between the primary and secondary.
As you can tell, this isn't stuff you can just do by fastening the parts to a vise and grinding away with a Dremel. Proper tools and jigs are a necessity. But with the right equipment anyone can do a great trigger job for a 1911. Brownells sells an
excellent kit for performing a 1911 trigger job. the kit also contains an instruction sheet that has a very well-done diagram of what proper engagement should look like, as well as some examples of bad engagement and the consequences. The instructions are
downloadable here.