Well I'm a fan of the S8 Plus which is my current phone. Had it pretty much since launch and it is a real powerhouse. But if you're looking for real power then why not wait and see what the new Note 8 will have to offer. I think you might be surprised.
Both are great devices. For me, the superb screen, camera and water resistance of the S8+ trumped the extra ram and dual sim of the OP5. But it's really a matter of whats most important to you as the guy using the device.