| There's some stuff on the Sigma site about this, and my info comes from the discussions I had with steve at MR about fitting a full 50mm system when mine went in for the SP conversion (I'm running Corse cam timing as well and had the offer of a very cheap Ti 50mm system).
I was advised against a full 50 system because I ride a lot on the road, so bottom / mid range is important and this would be affected with a full system, particularly bad below 5K. 45/50 for me only gained a marginal increase and wasn't worth the expense, so I bought mag wheels instead
45/50 was recommended for my setup , although DC since you're running an 853, you would probably be in a better position for running a full 50mm and will have no problems with a 45/50 system. | 
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