You've probably mentioned this already but: how many flight hours so far for you in the VC10?
Not very many, but increasing all the time.

Would you agree that transitioning to kerosene-burners requires some mental retooling (although I'll bet once you get used to it, it's much less skull-work than babysitting pistons)?
Yes, and that is where the sim helps out a lot. In my earlier flying training there was a lot of emphasis on being able to "keep ahead of the aeroplane", particularly when flying low-level, or leading a formation - thinking well ahead.
What I've noticed with a big jet, aside from the obvious handling differences, is the need to be way way ahead, planning far further ahead, such as briefing times for the descent for example. A lot more energy management comes into play too, and anticipation; with the jets you have to think a few seconds ahead with power changes, as it takes a few seconds for the to spool up; on a piston single you may start levelling off 100-200ft from the required level, in a jet, you start the mechanics of it 1000-2000ft from the desired level. After a while though it all becomes natural...
...I hope!
