What size stone is "too big" for a pendant?

Hahaha, I love that most of you are just like "too big?? ... What is this idea of which you speak?"

I have a blue topaz rough that should be able to cut a 14-15mm round and I've been weighing whether to have it cut down to more like 11mm, or just go full out and get the max size possible out of it. With other more expensive material, of course it would be cut for maximum yield, but for something like blue topaz that is really rather cheap in rough form, IMO, you can do what you want. Sounds like you guys all agree to go for the max, but I'm still a bit torn, wondering if a huge sparkly blue thing will make people think it's costume jewelry. Your enthusiasm has given me food for thought though!