Hi Johan,
As I understand it, you’ve added your Gmail account to your Outlook mail client, and your main concerns are about the Outlook client performance. (If I misunderstood anything, please feel free to correct me.)
Under this circumstances, I suggest you visit the Outlook IT Pro TechCenter for dedicated support. Currently, our community forum mainly focuses on Office 365 Online Services.
Thank you for your understanding.
Best Regards,
Allen