Mantis,
Depends on how big you are. A PPK or P-11, P9, etc., can easily run on the ankle of big guys, and the lighter P-11 won't even be that uncomfortable for 10+1 of 9mm.
"Average" guys might find the size and weight of even a P-11 (small and light for a 9) bothersome after a few hours, and if it's a 10 hour carry day after day, year after year, you might risk some permanent objections from your body.
"Small" guys better stick with P-32s (tiny and featherweight in .32 ACP), but all sizes tend to love the total comfort an adequate rig provides with it.
There are many ankle rigs available, and odds are that there's only ONE you'll be able to stand. Same way with an ankle carry gun.
Overall size and weight are the critical features of the gun. The heavier the gun, the heavier the rig has to be to carry it.
The smaller and lighter the better for an ankle carry gun. Remember, even heavier (by a couple of ounces or so) shoes can really fatigue you after a day of wearing them. There's just something about swinging around extra weight on your ankle that gets really aggravating after a few hours!
You can simulate how you're going to do by making a comfortable ankle weight of about what the gun and rig is going to weigh, and wearing that around all day for a few days.
All I'm sure of regarding ankle carry is that if you don't stay within the parameters of what your body will tolerate, you either won't wear the rig or you'll be grumpy and hard to get along with all day.
Choose well!