All 3 of my basses are tuned CGCF. A while back I started using a "custom gauge" set of SIT Powerwounds in 50 / 70 / 90 / 110 for that tuning. The 110 works fine for the low C, and has just about the same tension as a 125 tuned to low B. SIT will make "custom gauge" sets at customer request through your local dealer at the same cost (about $17/18) as a standard set.