Would like to try Topaz hop pellets for late additions (no dry hopping) to achieve a bit of "grassy character" that you can find in "Saaz" styled hops.
I have done it dry hopping in the fermenter, and the grassy character certainly comes out, but I want to have a turn around time of about 21 days with this beer, and would really like to have a decent volume extraction out of this beer.

I would like to use a California Ale yeast or a Kolsch yeast and ferment at a lower temperature to keep it really clean, so I am Ok with a longer ferment time, before I harvest yeast and condition.

Has anyone used a lot of Topaz hops during the whirlpool.
Batch size: ~20 HL (Castout)
OG: estimated at around 12.5ºP (Castout)