The current exhaust is rated to handle the temps. Its a Type L flex pipe which is suppose to be what it needs.
I dont think I would have any issues with pipe size but after more research it looks like I am going to run a seperate dual wall flew for the stove. I dont want the chance of any creasote causing a burn through in the flex pipe, which even though they say it cant happen, I KNOW it happens as we have had several chimney fires from that very problem.