i would guess that it would spine test higher, being dense. Similar in comparison from poplar to ramin dowels. I have footed poplar dowels with red oak dowels, and i think there was a small change in spine but it would depend on the length of the footing. If you could accurately read the grain on ipe you could make a few shafts and try them out, or just use them for footing. either way depends on the particular pieces you have available, and how the grain is. ramin 5/16 dowels usually spine in the 40-45 range for me,while poplar at 5/16 spines in the 30-45 range depending on footing and taper. i have a poplar dowel that is 3/8 with an oak footing that spines in the 75 lb range although it is pretty short, im expecting it to spine about 45-50 when its finished. it all depends on the particular wood and length i think,along with diameter. personally i feel better about footing with harder woods than using them for shafts, as they may be hard to straighten. also, if you build a hardwood shaft and it snaps in half all that works gone, whereas a footing you just put on a new footing. also helps with the weight forward.