Regardless of the finish, all the new 5" Sig 1911s are machined out of stainless steel for frame and slide with tight frame-to-slide fit and match grade barrel/trigger components that produce very accurate shot groups.
I have the railed TacPac and got verification
email from Sig Sauer that it is indeed the same pistol as TacOps without the ambi safety, night sights and mag well. I paid $850 for the TacPac and it is a nice value package that costs less than the TacOps with the inclusion of the compact laser and holster.
All of our 1911 models are essentially the same, yes. With the exception of the aluminum frames on our Compact models (RCS, C3, 1911U) everything is stainless steel and has match grade internals. It is the external paint schemes and controls & grips that differentiate them.
Only issue that I found is that if you reload SWC profile bullets, because the start of rifling is so soon with almost no leade, I need to keep the OAL short around 1.245" for 200 gr Missouri SWC bullet instead of more typical 1.250"-1.260" but this is not a bad thing. Because the start of rifling is so close to the chamber, chamber pressure seems to build faster for more consistent shot groups. With the 200 gr SWC and 5.0 gr of W231/HP-38, I am often getting dime sized groups at 7 yards and quarter sized groups at 10-15 yards off hand.
I have done comparison range tests with several other 1911s to include Kimbers, Colts, Springfields, S&Ws, Paras, RIA Tacticals and like many other shooters, found the TacPac to be very accurate on par or better with more expensive models. In my opinion, you are getting quality and accuracy of pistols costing $1000-$1200+ with stainless steel frame and slide even with the base XO/Nitron models that cost around $700-$750.
You can see detailed pictures of my TacPac here -
http://www.thehighroad.org/showthread.php?p=7624449#post7624449