How Many CFM To Cool 600w HID With Outside Air

My room is 3.5w x 7.5l x 6.5h. I'm currently running LEDs but I want to try HID on my next grow. The room itself is already vented with a 720CFM 8" centrifugal fan that pulls air in from the rest of the house and pushes out back into the house. There's also an A/C vent that pumps cool air directly into the room. I have to shut this during the winter to avoid overheating the room when the heater comes on. There's another vent that's completely passive intake (fan-driven) for when I have to close the AC one.

I'm planning to run a separate feed for the light. I'd like to pull air from outdoors via a roof pipe over the light and then into the attic. The outdoor temps can get over 100 in the summer.

Will this work at all? I hate the idea of using inside air to cool the light and then venting it outside since this will just cause hot air to get sucked in from somewhere else in my house. But, I don't know if outside air will be cool enough when it's hot outside.

Does anyone have any experience with this and/or suggestions as to how I should set this up? Heat is definitely an issue in this room.

Thanks in advance for any suggestions/recommendations.

We've gotten into the high 80s and so far, the light is staying very cool. I used insulated tubing and put insulation around the light so that it would dump too much heat into the room when the outside temps get higher. Will be curious to see how cool things stay when it gets hotter. I will update this in the future if I run into issue.