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Question

Shalom: What about those who say Shema within the z'man, without the brochos, before davening, and then go to a minyan? (On shabbos, for example) Is it better to say the shema with the brochos and the Amidah (s'michas geulah l'tefilah) and then go to minyan for Torah reading and Musaf? What I'm trying to ask is, is it more important to say Shema, with the brochos, in the earlier z'man; or is tefilah b'tzibur more important. Where I live, the shul davens on shabbos morning at a time where sometimes they make the Gr'a z'man, and sometimes not. They never make the M"A z'man. Should I daven through the Shacharis AMidah by myself and then go to shul? Or should I say Shema, without the brochos, and then daven with the minyan?