I've gained over 1 stops in brightness just by changing the glass screens in at lewast half a dozen cameras, closer to 3 stops when I've added a fresnel as well.

Over the past few years I've rarely needed to use a dark-cloth with my Wista although I always carry one and the same goes for my Grown and Super Graphic both of which have new screens alongside their fresnels and the added advantage of their focus hoods.

So you may want to get a brighter screen made.

Ian