I gather from the lack of input from the "crowd" on this issue that I'm dealing with something either very poorly documented or marginal. Worst case, both.
When I was first taking the old bearings out of the 2007 Adventure sprocket carrier, I immediately thought that "this is some shadetree engineering!" Perhaps somebody had ruined the original sprocket carrier and found an "alternative" cush drive to use, with a different size bearing housing. (This was not the case, as I was to find out later.)
This issue has bothered me much, as none of the fiches recognize this discrepancy.
So, I went on to find out about it myself.
I had a discussion with a bearing expert, who basically confirmed my suspicions about the performance of two deep groove ball bearings stacked vs. an angular contact ball bearing. In this application, the angular contact ball bearing will support higher axial loads than (even two) regular ball bearings. Now, how much axial loading is actually imposed by the asymmetric chain drive? Is this axial load over the design specification for two regular ball bearings? These questions cannot be answered without further analysis and calculations. The alternative would be to get in touch with the design engineers at KTM and ask them directly.
I then talked with someone who has access to the dealer fiche tools. In that fiche, the same mistake was found: the rear sprocket carrier bearing for the 2007 LC4 Adventure is specified as 0625032057 GROOVED BALL BEAR. 3205.B.2RSR. However, searching with the VIN code of the bike, a different number was found for the sprocket carrier bearings: 0625060058 GR.BALL BEAR.6005 DDU2CG23S6NM.
Some more fiche work on both sides of the counter produced the following. The 3205 bearing (and consequently, the 58310050144 SPROCKET SUPPORT CPL. 03 sprocket support) was used from 2003 up to the 2005 LC4 Adventures. The next iteration of the sprocket carrier (58310050244 SPROCKET SUPPORT CPL. 05) is in some fiches shown to fit 2006 625 SMC's. The fiche for this SMC also shows (correctly) two of the 6005 bearings in the cush drive. The third iteration (58310050344 SPROCKET SUPPORT CPL. 06) is shown to fit 2006 and 2007 LC4 Adventures, but unfortunately these fiches incorrectly show one 3205 bearing in the cush drive.
So, why did KTM go and change the cush drive design? Was the switching from an angular contact bearing to two ball bearings done in search of a performance increase or a cost reduction? This one is not too difficult to guess...
All in all, it remains that the (public version of the) spare part documentation could do with some updating and error-correcting.
I don't know whether the new bearings are inappropriate for that position. The 2007 ADV has about 15tkm on it, and the sprocket carrier bearings were crunchy, which started this whole saga. My 2003 ADV has 30tkm on it, no problems with the sprocket carrier angular contact bearing. However, failed 2005+ LC4 ADV cush drive bearings do not seem to be making headlines here or on other forums.
If the newer sprocket carrier design allowed for easy switching to angular contact bearings (with a similar dynamic load rating as the 3205), I would probably consider it. As it stands, though, the stock double 6005 setup will be tried again, until the next failure.