7/16" is really huge for a P19. Most of the people I know (including myself) are using 5/16" line with a fairly smooth cover (read: Dyneema Racing 2). In the last race I sailed in though, I used 7mm Robline Racing Sheet (similar to Maffioli, but much better) with 3/16" Spectra spliced to it where it runs through the blocks. It worked perfectly, and I was very satisfied with how the friction was reduced. The smaller line didn't hurt because it was a very "grippy" line. Check out Robline Racing Sheet.