Rob I own 10.5mm and 14mm Pentax XL's and can relate to your experiences re contrast vs the naglers. A good few months ago when Saturn was still around I had the opportunity to compare my Pentaxs with a large selection of naglers.
I was finding my XL's barlowed were bettering the equivalent type 6 naglers unbarlowed in terms of scattered light, and equalling them in sharpness given that both were limited by the seeing, which was better than average on the night.
I do own a 31 nagler and know what you mean about the field curvature, still I love it
Conclusion: Televue isnt the only show in town at the top end of eyepieces.