I'm using a box of spiral BLBs very similar to Martins - same sockets, bulbs vertical. My bulbs are only about an inch and a half above the printer glass. I'm using 15-watt bulbs as I can get them locally. Exposures on negatives made for the last Grade 2 Azo run about 10-12 minutes, so I don't believe the unstable warmup period makes much practical difference. I'm able to get repeatable prints in VDB.
juan