Depends on the engine, fuel system, power levels, intercooler efficiency, etc, etc-- e.g. if you go get a Ford Racing supercharger for a mustang, the stock ecu flash will have you around 13:1. Paxton blower on a Viper, around 12.5:1. Both make huge power for the amount of boost, and are completely safe on pump gas. However, both run on relatively large displacement engines with relatively little boost and timing.
On a small displacement, high boost engine, you want a richer AFR. I have holed pistons running ~12-12.5:1 on a 3S on a road course in hot weather, on 100 octane race fuel. That AFR may be reasonably safe for a street driven car that only sees full boost for prolonged periods once in a blue moon, but it's not worth another 10-20 hp to risk melting your engine, in my book.
11-11.5:1 is much safer, you can run more timing and the tune is more forgiving to atmospheric and fuel variations, of which there are a LOT in pump gas.
As for timing, it again depends on all the other metrics of the engine and power goals. If you're running a stock stroke 3S at ~15 psi, I would probably start with 10-11 degrees of base, 30-35 degrees under light load/boost, and pull it back to ~15-20 degrees over 5 psi or so.
Those are very rough numbers, of course, and you'll have to dyno tune your timing based on knock and other factors, and leave a few degree margin of safety for temperature and fuel variations.