IAM "Skill for Life" course...recommended?

[Grahamm]

That seems to blend filtering and overtaking into the same thing.

I'd say they were different subsets of the same skill, it's just a matter of speed and positioning. Another piece of advice is to treat filtering as an on-going series of overtakes.

So are we saying that overtaking into oncoming traffic is ok if slow enough. All city rush hour overtakes involve oncoming traffic.

As mentioned, it's only a no-no if you make someone else feel the need to take avoiding action. Coming back from my holiday yesterday there was a long line of traffic approaching a pedestrian crossing so I took several opportunities (not to mention great delight ) in moving into the opposite lane and pass several cars in one go, then making a pre-planned drop back into a gap between the rear of one car and the front of another when there was traffic coming the other way .

Also doesn't not making progress and riding within your limits and comfort zone contradict each other.

Nope, because as you get more practice and experience you find your limits increase and your comfort zone gets bigger