Rationally managing fear is self preservation at it's best. Having no fear and irrationality handling fear can be equally as dangerous.
Being comfortable at 20' but not 40' is a bit irrational in my opinion. A fall from either height has the potential for the same consequence. I also believe by limiting yourself to those heights you are limiting yourself to work a tree safely. One of the best ways to learn how to safely work a tree aloft is by taking smaller bites. Taking 20' of top 60' off the ground is generally safer than taking 60' of top 20' up. Work your way up to the big cuts by working your way up the tree.
The best way to get comfortable is to spend time climbing. Do as much rec climbing as possible that way you can take your time and not feel the pressure of production.
I think you may have a niche in your market if you keep your overhead super low where you can take small jobs. It sounds like the other companies in your area simply cannot afford to be competitive in that respect. That said, do your research and try to anticipate all of your costs upfront. Getting into the treework game can be extremely expensive. There is a huge gap between the guys with a truck, trailer, climbing, cutting tools and a full on tree service.