No the issue with IR is not loss of detail, you can always use hi-res IR map, which yields better precision, but not better quality. It will simply always create artifacts in far-off scene due to sample allocation, detail enhancement isn't there to solve this issue, LC retrace partly is. Scenes like Parisian apartment, could not be rendered in IR even with lowest Normal/Distance thresholds in IR, the algorithm itself, simply fails at such geometry and detail enhancement doesn't reach those detail in far-off parts of scene, only BF does.
10 hours per dual-xeon slave for 3k is a lot, esp. if you say it doesn't even converge. Like I said, mine are half of that, which I still consider too much, but double ? That's rather extreme... Do you use some un-orthodox lighting setup ?