The question is “What are you more afraid? to be in the small side or in the big side?” If you are afraid more to turn up too small and less afraid that it’d turn up to big, then go with the bigger side. (and the other way around if you are afraid it’d turn up too big more).
For example me I was between 285 vs 300cc.. I was more afraid that they’d turn up bigger than what I was scared of smaller.. so I chose the smaller 285cc.