The No. 5 Jungle Carbine (rare, but still available) is based on a lightened No. 4 receiver, with a short barrel equipped with a flash hider, and a cut down stock. It is equipped with a rubber buttpad because the reduced weight results in more kick. Some have found it objectionable, but I don't think it's too bad. The REAL No. 5 has a reputation for a "wandering zero" problem, where the point of impact moves around in relation to the point of aim. This has been associated with the machine work done to lighten the No. 4 reciever. Gibbs makes REPLICA No. 5's based on unaltered No. 4 receivers, so this shouldn't be a problem.
The No. 4 Mk. I and Mk. II are WWII era rifles. Lots are out there in various quality
The No. 1 MkIII is the original WWI era rifle that was made up to and through WWII. It's a beefier action. All of the above were chambered for the .303 British cartridge.
The Ishapur arsenal in India manufactured a No. 1 MkIII action with much improved metallurgy that could handle the higher-pressure 7.62 NATO cartridge. This action has been used by Gibbs to make the No. 7 "Jungle Carbine" which was never actually issued.
The biggest difference between the No. 1 and No. 4 actions is the location of the rear sight. On the No. 1 it is ahead of the receiver, on the No. 4 it is on the back of the receiver. IMHO the No. 1 looks "clunky". Both use 10 round detachable magazines but were designed to be loaded with 5-round stripper clips. The box was detachable to make replacement simple if it was damaged.
I've owned one real No. 5, and two No. 4's. I've never owned a Gibbs. My No. 5 did not evidence any "wandering zero" problem. None of my Enfields are what I would consider accurate. I've heard of some that were, but I haven't witnessed one myself. Still, I love that damned old gun, and I'm STILL looking for one that shoots better than 4" at 100 yards.
Before I bought a Gibbs, I'd go looking for a good surplus No. 4, unless you really want a .308. I've heard good things about the Gibbs .308 rifles.
If you're interested in the Ishapurs, try: [url]http://www.ishapur.com/directory.htm[/url]
For general info on Enfields, try: [url]http://pub42.ezboard.com/fparallaxscurioandrelicfirearmsforumsfrm49[/url]