Yeah the 800mm ad 700cc road might be better, if you are thinking of a new barrel anyways. I just tried to cram everything into the old barrel lenght and I am not sure that I am happy or not. I would have to do more competitions to really find out.
I was wondering if you had a 500 mm FX impact barrel and you wanted to increase it to 600 mm can you just buy the liner and just get a barrel extender to save money?