Dave, I must not have had my thinking cap on yesterday. Robertson's has a 7/8 in their booth, you can bring your prospective endpin right to it to see how it looks. 30 mm, I'll guess you're looking at a carbon then? Ask Nick Lloyd there at the show what he thinks of them, you'll probably find him at the bar.

It's risky for a luthier to say that one accessory can make a big tonal difference, but he was very impressed when he installed one. No idea what pin he used, but I think it's on his competition bass.