| I've owned a 996SPS and currently own a 996R.
They are both great bikes, closer in performance than you might expect except for the 9,000+ rpm range where the R wins,whereas SPS is a bit stronger in the midrange, according to my dyno readings.
The newer 'stretta engine in the R maybe a little more durable in terms of rocker wear, better oil feed to the top end.
If all things are equal i would go for the 996R, but would in noway be disappointed to have another SPS.
The deciding factor would be which bike is in the best condition with the most comprehensive service history from a reputable/knowledgable specialist.
I would be a bit wary about buying off ebay myself without the benefit of a thorough inspection of the bike. Worth seeing if you can view them first before bidding.
Good luck. | 
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