[Wannabe]

I'm in a similar boat to you and I've decided to go larger, too. I'm using a DIY rig and have never filled the cones, but it seems to me that using a too-small diameter may inhibit overall growth. I think the only time the volume matters is once you do actually fill it. I'd pay more attention to cup diameter. As long as it fits your entire breast area, you should be fine. In fact, as I said, I think it probably works better with larger than smaller cups (as long as they fit OK).