Can anyone tell me the effective guide number for the R1C1 with two SB 200 units in use? Each unit has an apparent guide number of 10? Many thanks, DaveG

Doubling the flash output (by using twice as many flash units) would increase your output by a stop which equates to 1.4x the distance. So the GN would go from 10 m to 14 m when both SB-R200 heads are used.