Hello from Finland, my first post to your excellent bow forum!
I know a this guy (known as sumpitan in pa) from here (Finland), who uses and has used a lot of prunus padus, bird cherry, and really thinks its good bow wood. I think he has been building bird cherry flatbows for about 20 years now. Well not only bird cherry bows, but you may understand that its not bad wood if you have been making bows from it that long...
Bird cherry is soft, but what i have heard, its really tension strong. So toasting the belly will help the bow greatly (i assume). It will make good flatbows, if you have right dimensions - aka enough wideness. The bows from bird cherry what i have seen, have been about 40-50# tops, but also shorts. So not that high poundage, but if you go longer and wider, higher is possible.
I just cut my own staves recently, and i am also trying some longbows from it.
I can give you couple of links to our finnish primitive bow forum, where you can see some pictures of bird cherry bows. Ill translate some dimensions here, cause the forum is in finnish.
http://perinnejousi.yuku.com/topic/128/Btuomi-ja-tasankonuolet130cm/52" ttt, 32mm wide, natural B-profile, 37#@21".
Cut from just a little thicker tree than the bow.
bow by sumpitan
http://perinnejousi.yuku.com/topic/100/Tuomilyhri140cm/55" ttt, 40#@24", handle 30mm wide, at widest 35mm, 12mm nocks
Hope this helps!