I had the same dilemma. I chose "proficient" because I'm sure there are any number of people out there who would tell me I hardly qualify for highly skilled.
I mean, sure I'm reeeeally smart, but my background has no robotics, no metallurgy, no chip design, no ergonomics, no software design, etc.
Not saying I couldn't design the computers. Just saying I probably couldn't program them (though I am sure I could quickly learn to), nor could I design the vehicles (this would take me longer to learn).
And hey, I'm getting better about accepting praise. It's tough, though. I have a reputation for arrogance to mitigate.
...I'm deathly serious about that last bit.