Ironically, I just got an email from them asking if I was a brush user and to take their brush survey. I can't find it so I think I accidentally deleted it!
The Vic Firth Jazz Wire Brush (Model WB-White Plastic Handle) has a pretty thick gauge. Vic says it's medium gauge on thier website, but I find it it to be on the heavier side. I think it's way too heavy and loud for light jazz, so I think it's ironically named. Most jazz players that use Vic use the Heritage Brush (Model HB-Purple Rubber Handle)
I know the Jeff Hamilton signature Regal Tip brush had thick, heavy gauge wire. He is now with Innovative Percussion, and it looks like his signature brush with them is also made of stiff, heavy gauge wire. Those are the two heaviest and "loudest" wire brushes I have ever used. To clarify, I own the Regal Tip Hamiltons, but I have not used the Innovative Hamiltons. I would imagine they are virtually identical.