I posted a question about 304 vs 316 wire on the Brion Toss forum "Spar Talk" as follows:

"When replacing standing rigging, what are the pros and cons of one type of wire over the other. I understand 304 is stronger and cheaper, but 316 is more corrosion resistant for salt water. However, the boat is sailed on the Great Lakes."

I got this response from the man himself:

"Hello,
Get the best quality wire you can, of either alloy. You don't need 316, but if you could find a brand of it that had breaking strength comparable to 302, and if this wonderful wire actually cost less than most 302's, that would be the stuff to get. As it happens, that is the wire we sell...
Fair leads,
Brion Toss"

Very mysterious. I suppose he's trying to keep business for himself (yet won't respond to your requests for a quote). We can probably assume he only uses one type of wire--his "special" 316.

He's throwing another dimension into the equation: the quality of the wire. I think I'd be comfortable with BoatUS. Just for kicks, you could ask them the manufacturer and rated breaking strength.

Are you using the procedure where you send your old rigging to them and they duplicate it? Sounds like a good way to go, since errors of measurement can be a big problem.

To that end, you might want to inquire about the turbuckles. I've seen two different sizes used on our boats, one larger (thicker) than the other. Thicker turnbuckles can also be an inch or so longer.

The equiptment list in the Manual specifies 3/8" pin diameter turnbuckles. They may be trying to sell you 5/16" (about half as strong).