It's fine. It's always OK to mix oils. "Synthetic" oils like Mobil 1 5W-30 are already a blend of Group III, IV, and V oils.
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'10 PW 370Z 7AT - wife's car - Project Raspberry Cheesecake
'08 Evo X - built motor+trans | BB-X @ 32 psi | CH3OH | self-built+tuned - ??? WHP
'01 Galant V6 - built motor | GT35R | self-built+tuned - 550+ WHP (retired)
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