Thanks all! Not sure the speeds, but I'm sure they weren't as high as I hit the week prior on a FS rig with actual disc brakes (but absolutely the wrong tires).
I have to give thanks to Alan Bonds for inspiration for the bike. It was originally built as a Larkspur Canyon bomber analog using a Morrow coaster rear hub and Suzue BMX hub up front sans brake. I used AB's website as my cookbook to build it, changing a few things along the way.
I raced that bike once with the coaster build on a local DH/Super-D course near Monterey and missed the podium by one spot (4th). The next race I had these wheels and was on the podium. But that course was much less steep, and the brakes had a chance to cool between turns, although the speeds were every bit as high. However on the lower part of Repack, I was losing the brakes due to the consistant steepness of the hairpin section. They were cooked. I couldn't have stopped the bike at all in any reasonable distance.