Adding numbers increases the paint time by about 50%. They are put on the needle layer, and thus they are "see through" . If you wanted to have a background to the number, like maybe an odometer-style thing, then you'd add that to the static background.
Speaking of which, thanks for prompting me to try this all-on-one-layer thing, I'm quite pleased with the speed improvement compared to having each gauge on its own layer, even though I haven't had the performance challenges with my apps that Scantech's having with his way more complex one.
As much as I enjoy programming, I'm going to call this issue:
job done.