The main design difference is that series 80 guns have a firing pin block that works with the trigger. This feature usually makes the trigger pull a bit rougher than desired. Series 70 guns generally tend to be fitted and finished better as well so they demand higher prices on the used gun market. These statements apply to Colt pistols only.
If you are in the 1911 market, there are a lot of other makers besides Colt and most of them are making guns of better quality. Just like with trap guns, the sky is pretty much the limit on what is available, perhaps if you think up a budget number we could steer you towards a few 1911's worth looking at.
Kimber, Baer, and a bunch of others in the US make fine 1911's. The previous writers are correct in their description of the differences. I have a series 80 in 38 super which has a pretty good (not match grade) trigger. If you can see it clear to do so, you might want to look at the Taurus PT1911. It has many of the upgrades already built in and has a street price of around 500-600 bucks. To do all that it already has to a stock milspec you'd spend 1500 or more. They shoot pretty darn good. Otherwise, as the guys said, prices begin at somewhere around 400 and go well into four digits for the really good, fancied up stuff. My brother has a Kimber match that he bought new a few years back for around $1200 and shoots with the best of them.
I'll second the Taurus recommendation. I bought my son a PT1911 in stainless steel for his birthday in October at a gun show for $600 and liked it so much that I bought one for myself two weeks later from the same dealer. They come with a lot of the stuff you'd add anyway - decent sights, ambidextrous safety, skeletonized trigger and hammer and some other goodies - and shoot pretty well.
They may not be the "best" 1911 out there but they are a lot of gun for the money. We both spent $50 having the "liability" triggers smoothed and lightened to 3.5 pounds but that's about all they need to be good shooters.
I had a Colt 1911 series 80, had some work done on it but never really ended up liking it or it's accuracy. Traded it off for a SS S&W 1911. My Smith is head and shoulders above the Colt. I'm a lefty and the Smith came with ambi safety along with adjustable sights and nicer grips plus it just feels and shoots better. It's well made and works flawlessly.
The Springfield you mentioned is a better buy than anything offered by Colt these days. What are you looking for Trapshooter? Something for CCW or recreational shooting or ....?
Take a look at the SIG line. They have all kinds of well made autoloaders including a 1911 platform. Very good values with all their guns. The S&W 1911 mentioned above is getting alot of good reviews also, none of these pistols are exactly low cost.
I bought a S&W 1911 performance center model for 1350.00 new. Very nice gun. Smooth action shot anything I put into it. Only on a very limp wristed shot would you ever get a failure to eject/feed issue. I traded it for my current XT trap gun. Secound thoughts on that trade! Love my XT but miss the PC 1911. Trigger was very good. Not a good carry gun way to light of a trigger.
Thanks guys for all your input. It has helped me a lot. I will have a look at the others mentiooned before I do anything. I never thought about a Smith or Sig, but will definately look at them too.
Its always nice to hear from someone who has had first hand experiemces with something rather than someone pretending to be an authority on something from hearsay.