On the first RV-10 I used the James cowl. I consider this cowl the best modification I did on that plane. Talking with the new owners of James Aircraft they are working to offer an RV-10 cowl again (and an RV-14 cowl) but no timeline in place. Im looking at the Show Plane cowl as a backup plan.
The James Cowl uses a 14 spinner. At the time Hartzell wanted $1400 for a polished spinner. I found a kit plane place that uses the same spinner on their kits and got it for $750 (shipped direct from Hartzell so it gives you an idea on the markup).
For me, the stock Vans cowl and 13 spinner is just out of proportion for the RV-10. The new plane will sport either a 14 or 15 spinner.