1 1/4" is fine for a 60# Ipe bow. One thing to remember though is that the larger a board is, the more likely it is to be unstable when cut up (ACCORDING TO MY CURRENT OPINION/ OUTLOOK). So if you go 1 1/2" wide, it will give you some leeway if the board warps for laying out your bow. Your board looks good to me, you can avoid that knot I'm sure. Ipe does make finer dust than woods like hickory when resawn, which is annoying. I run two hoses off my shop van to my bandsaw, one at the normal hook up, and one to catch all the dust that the bandsaw shoots out under the table for woods just like ipe. Some people get really bothered by the dust. I don't mind too much, and I have asthma. It reminds me of bitter unripe almonds for some reason,
. But be sure to wear breathing protection, some people the dust will even irritate their skin.