I would try to get a tire with more volume for bumps and irregularities in pavement surface. At speeds over 15mph those tires may cause you to bottom out pinching the tube, but worse yet losing control from a harsh jarring could cause you to fall. It's your ride and I'm not trying to tell you your business, I just would be real careful how you ride at speeds over 15mph.
I will be running 1 3/8" wheels and tires also. I agree it is going to require some common sense and a little extra care while riding. Mine are designed to run at 55 PSI, which is pretty much rock hard, for moderate non-performance riding they seem ok. My test runs have gone fine.
yes the tires were hard. the thing was twitchy. but it accellerated very good. I hit rocks and blew the tires several times then the whole thing started feeling loose and the frame was giving so I scraped it and built my red rocket. It loosened up the same way. so Now all my goodies are on a BFGoodrich scwhinn.
I am going to build another. this time I plan on using a cannondale or simular bike. a very tall one though. Use some of those thorn proof tires a kickback and down seat post and straight handle bars. some sort of cylindrical tank mouted under the top bar. It will be my speedster.