Anywhere from 3 foot to 6 foot would be fine, although if the line has high elasticity, something on the shorter end would be better. Super short is doable, so are prusiks. 5" eyes and up will give the most accurate results due to the bend radius that will result, although if you want tight eyes tested I'll just find carabiners with a stronger break strength and clip them onto amsteel slings. Should be no problem.
Let me know what would be useful in terms of report. What it broke at, obviously, but I could also take pictures of where the splice failed so you don't have to pay to return it (although I know a lot of guys like to feel it in their hands).
You guys do good work, even a cursory glance around this forum makes that pretty clear. Consider it a professional curtesy; If I can help out in any way, I'd like to. Especially with safety being so important.
Ian