The biggest issue I have with buying severely over-rated cells from eBay, is that most cheap bargain cells are not consistent from cell to cell. This is a problem as cell consistency in multi-cell devices is a very important factor for cell health. Cells from reputable manufactures are generally all going to be within a couple percent of each-other capacity wise, while cells from "oddball" sources, especially those with huge numbers printed on them, are more apt to have variances of 10-20% or more from cell to cell in capacity and internal resistance.
Cell consistency problems in "bargain" brand NIMH cells is a well known issue, SilverFox may be able to speak more to the issue than I can, but I have enough cheap cells to know they were a waste of my time now.
I'd rather pay $3 for a cell that delivers hundreds of trouble free maintenance free cycles than $1 for a cell that develops problems within the first few dozen cycles.
Currently, for high capacity cells, the Sanyo 2700 is probably the way to go, but as with any high capacity cell, it'll need to be treated with tender loving care, including proper charging and maintenance cycles, in order to maintain decent capacity through it's useful life. Abusing high capacity cells with heavy duty loads seems to be one of the fastest ways to cause their self-discharge issues to get really bad really fast.