From personal experience you don't require 5' of swing room to slash effectively with a bladed pole weapon. About 1' will do it. Remember this isn't a baseball bat thats being swung at a fast moving ball, its a blade at the end of a large fulcrum. By using the back arm of the swing you can easily and effectively generate a lot of power, more than enough to cut through armor.
I've knocked guys over with about a foot of 'swing' by using my body wieght as leverage.
As to thrusting tips on poles, its easy to see why most pole-arms have them, they are very useful without much effort. You can simply place and push with your body if you want and it will penetrate. Or you can 'rock' your arms back and forth for a nasty punch type of thrust. I prefer the 'slash and bang' where I slash at an opponents head (he blocks it) and I pull back using the momentum from the swing to power a thrust. It's a really quick way to score a hit.
Oh...I've been fighting primarily with polearms in the SCA for over 20 years (thats how I know about hitting folks with em). I've used 6' long glaves in castle battles (narrow confined spaces) to great effect (much better than using a sword that has to be swung to gain power). Remember that leverage can create a lot of power in a small swing and body wieght applied to the weapon is also very effictive.
Oh..and lucern hammers and bec's, they are pretty nasty in a close in fight (two handed swinging), but even more useful when used in concert to someone who is pulling down an opponents shield for the hammer guy. They don't require a huge amount of power behind them due to their sharp points and weight behind the heads. I believe they saw a lot of action at the Battle of Visby, as dozens of the remains there showed a single square edged puncture in them (usually the skulls but also on some rib cages and femurs). An old buddy of mine was into archelogy and had these very interesting photos of the digs there.
As to shortening up on a pole to use in close; it is easy to do, to a certain pole length (say about 2' longer than the users hieght) after that the pole end catches on the ground and is much less effective when swung (remember its dragging around) thats why I use a 6' pole most of the time, its got reach (about 8' when thrust) and I can easily shorten it up to fight and defend against close in attackers.
cya