Roll on Single or Double rate up?

If it doesn't matter much to you which of the two you'll get, go for the double. Otherwise, go for the solo. Roll for who you like most.

I haven't paid attention to the odds when there's a double rate up, but for example, when there was a triple rate up, each of the 3 had a 0.3% chance, meaning that the odds of getting any of them was 0.9%. Thus, the chance of getting "spooked" was only 0.1%.

If the odds on a double rate up are greater than 0.35% per servant, and it doesn't matter to you which it is, then I'd go with the double to give the best odds that you'd get either and not an unrelated servant.

If you want both, go double.

I'd say the double as well. I mean if you went just Arthur, Ozy would still have an chance to spook you not being an limited servant but since you want both anyways why not.