Ireland Engineering used to have 9.5:1 forged pistons They were Mahle knockoffs but I think they had problems with the supplier and no longer offer them. They offer custom made forged pistons for $650 a set Do a little research about pistons and you will find that for most street applications, cast pistons offer greater affordability - since you mentioned it - and practicality in use.
As kbmb02 has eluded there many factors to consider in an engine build. including head height , block height, camshaft overlap etc.
It doesn't sound like you have the motor apart yet and don't know exactly how much oversize you need. It may be safe to assume you need the second overbore, but you wont know until you have the motor apart and the blocked checked
Don't rush into pistons without having a clear receipt for your motor build.
9.5:1 pistons have a very good chance of working well with California 91 octane gas regardless of the other details They just give a better margin to work with all the other components of the motor I've built two 9.5:1 motors in San Diego with no detonation and very pleasing results. The difference in power between a 9.5:1 compression motor and a 10:1 motor will not be significant, that's why I favor 9.5s
I notice you are local so PM me to exchange contacts and we can talk about this if you like