Ading one or even 2 cells at 10S makes very little difference in AUW but great power boost. It's a pretty low kv motor to handle it if you manage well your throttle inputs. If you worry too much about the extra weight add on little wing tips to reduce w/loading with a bonus of getting extra stability.
I have upgraded one of my E/F Fantom from stock 6S to 7S, making all the difference, with a unique set up, sling shooter with the main gear on. (pic)