Sit and spin rather than stand and grind?
That's kind of dependent on having a low enough gear to "spin". Personally speaking, if I were to "spin" (which I take to mean > 90rpm) up a 10%+ gradient I'd need a gear so low that my progress would be almost imperceptible, and I'd topple over.
For me at least, on a decent gradient, it's a choice of sit and grind or stand and grind. My 1:1 bottom gear is too high for me to spin.
This Saturday I was going up a local hill (Hogtrough) that's hill is steep enough that I
have to stand, I can't really get up it without standing. I spied a guy pushing his bike up ahead. I did finally catch him because he stopped for a breather, but before that I'd swear he was opening up a gap on me.