I'm pretty much the same as you --- the best description of my method would be "closest available finger". I can type at ~150WPM for long periods of time without any strain or tiredness, can reach 200+ in short bursts, and have done over 50WPM with only the left hand.
However, one thing I've found that really affects typing speed and comfort is the key travel and actuation force; I think a "light, spongy, bouncy" feel is best. A light force reduces strain, sponginess is a good cushion, and the bounce helps speed up the return stroke. You can type a lot faster once you train yourself to not try to await any tactile feedback, but just "trust" that you've hit the keys and they've actuated.
I am the same way. I always attributed it to early experiences learning to play the piano. The muscle memory is in your whole arm/hand/finger about the location, and the sequence of fingers is dependent on the sequence of keys that follow.
Agreed re: key feel. I learned on an Apple //e and still think that's ideal. MacBook keyboards are the worst for me... the constant tactile feedback I think creates a negative feedback response that overtrains my fingers, leading to weird typing mistakes. Switching back to a mechanical keyboard helped.
Thats why I like Cherry MX black switches (heavy accentuation force, linear without click). You can basically tap them very lightly and type without bottoming out.
I am a bass player, so my finger muscles are very strong and I a little more resistance others may prefer red or silver switches.
For me it's just like... my brain knows where the keys are, and my fingers know how to move to where they're needed. I do have to look when typing one-handed, but it's more to help "aim" that to search for where the keys are.
However, one thing I've found that really affects typing speed and comfort is the key travel and actuation force; I think a "light, spongy, bouncy" feel is best. A light force reduces strain, sponginess is a good cushion, and the bounce helps speed up the return stroke. You can type a lot faster once you train yourself to not try to await any tactile feedback, but just "trust" that you've hit the keys and they've actuated.