Hi Tqualizerman,
Some people here have tried things similar to this - perhaps PM those within these threads, that mentioned they have tried what you want to do, :-
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http://forum.x-cart.com/showthread.php?t=30244&highlight=test+ab
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http://forum.x-cart.com/showthread.php?t=39507&highlight=google+test
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http://forum.x-cart.com/showthread.php?t=33403&highlight=multi-variant+testing
Hope they can provide you with some feedback (personally be interested on what you decide to do - so do feedback here if you can?).
Cheers - Asiaplay
PS: just be careful of duplicate content if you test two sites for different skins only...
(i.e. if content is too close then one site will get indexed and the other not... which will bias results).