I can't offer much at all.
Shadoe had her dental and went from 10Lantus to no shots to 5u Lev because of her low numbers more than because of the difference in insulins.
Oliver switched when his numbers were so disgustingly high, and his dose was still low at 4u, so we switched 1:1.
I think often people suggest a bit lower for the switch, just in case. After all, better to give too little than too much and be all stressed trying to bring up an acro. And if you have a stubborn one, you don't want to be trying to bring the numbers up.
Better to go low, because there's always more where that came from!
Best of luck on the switch; I haven't had any regrets.