Thanks for all the feedback guys (I'm the OP), it really helps to hear others opinions and personal experiences...keep 'um coming!
Glad to be able to help.
- I would like a 16" barrel so that leaves me with either carbine length or mid length gas system (DI - not piston). Several have mentioned that the mid-length gas system does indeed offer real world advantages (now where do I find one of these midis?).
Definitely go with a mid-length system, they do not cause as much excessive wear on parts. Any respectable AR manufacturer should offer a 16" carbine with a midi system. I wish I could give you a defenite answer, but you will need to shop around a bit.
- I would like a chrome lined barrel (I think?). I read that the service life of a non-chromed barrel is much lower than I expected...I want it to last many years at an estimate of 3,000 rounds a year. So how long will a non-chromed barrel last (gas port errosion?)?
Chrome lined barrel and chamber, definite musts for hard-use. At 3k a year, expect barrel life of around 6 or 7 years (20k rounds). I may be a little off, so if anyone knows better, feel free to correct me, please.
- I'm torn between 1/7 and 1/9 twist rate. Realistically 90% of my shooting will probably be with the cheap ammo which tends to only come in 55 - 62 grains. However, I realize that 1/7 gives me the ability to stabilize the heavy stuff, but how will it do with 55 grain?
1:7 can cause keyholing with lighter grain rounds; 1:9 is probably the best compromise, and you will be able to shoot everything fairly well. Personally, I favor 70+gr rounds, so 1:7 is a must for me.
- if I get 1.5 MOA with cheap ammo, I will be a very happy camper, it seems I have under estimated the AR accuracy potential!
AR's are generally very accurate platforms. They have tight tolerances and few moving parts when compared to other systems, so the rifle may very well shoot better than you.
- I want a rifle that is reliable, and doesn't continuously break parts (I realize they all break eventually). Do I need to buy from top tier manufacturers (Colt, LMT, Noveske) to ensure that I get reliability and durability?
This is a tough question to answer, as everyone has a different opinion, but in this case, I think the old standby fits well: you get what you pay for.
Hope that helped.