The trigger pull lengths are exactly the same on the Series 70 and the 80.
In the early days of the Series 80, some people thought that you couldn't get a good trigger pull with the firing pin lock system.
After good gunsmiths proved that you could, most of the anti-Series 80 complaints stopped.
In fact, VERY few people can positively identify a 70 or 80 Series trigger pull in blind tests.
There's more variation in individual guns then in the difference between a 70 or 80 model.
Other then the extra parts in the Series 80, there's no legitimate downside as long as you don't botch it up when reassembling the gun after a 100% strip.
If you fail to assemble it correctly the firing pin might not unlock, the gun won't fire, and the firing pin and firing pin lock will be damaged.
The assembly is simple. Unless you're a total incompetent and not only reassemble it incorrectly, but also fail to CHECK it to insure it's right, there's no problem.
If you just don't like the Series 80 firing pin lock safety feature, it can be removed. To do so you'd need a special spacer to fill in the spaces the frame parts are in and you'd need to remove the safety lock plunger from the slide.
There are no other Colt autos that use "Mark" as part of the model identification.
The Mark IV is seen as the fourth revision of the Colt Government Model design and the first time Colt used the Mark identification.