Don't know mate but it is worth a try.

I think the rule of thumb is that you go up a gauge with every half step you tune down.

So... for the 7th
9s = 52
10s = 58
11s = 65
and the bottom end of the baritones is:
.014 .018 .028 .038 .050 .070
which should be OK though you'd have to mix and match them with another pack of regulars.