Lager fermentation question

I pitched a 1048 OG pils two weeks ago using a 500 ml slurry of WLP833. I checked the gravity with a refrac and its at 6.8P (1015). It's been at 48F the whole time, including time of pitch. I plan to use the yeast cake for a 1070 OG bock. I'd like the pils to come down a few more points, as it is only 69% attenuated. I've heard that yeast vitality significantly reduces at 4 weeks. Is this true for lagers? At colder temps? So I'm wondering if I should let the primary sit for another week, which would put me at 4 weeks after the D rest and cold crash or, should I do a D rest now, so the cake will only be 3 weeks old after D rest and crash (but will the beer drop a few more points?). I plan to pitch the cake into the bock on brew day.

Do a D rest now. Raise the temp 10F. If the yeast have anything left in em, that's the way to get it. Don't worry about the viability, you've got TONS of yeast to work with.

I like your way of thinking, git 'er done!!!

Thanks for the input.