As I'm beginning my journey into controlled lighting I took my Sony HVL-F43AM outside on a sunny afternoon, put a model under a canopy (shade), and wanted to see if I could get enough light out of the off-camera flash to get a blown-out background. [Clarification: My intention was to let the direct sunlight blow out background, use the shade to take the sunlight out as a key light on the subject so I could instead use my flash as key, and then use a combination of reflectors and ambient to fill. I was shooting around 1/200 and initially had my flash at full power firing through an umbrella, but I didn't think about the flash's distance: I left it something like 15' away from subject!]
Turns out that even in shade my flash at full power couldn't make a dent in the ambient light, even with no modifier. (I did get a measurable amount of fill using a 4' x 8' sheet of white coroplast as a sun reflector.)
Now this was with a Guide Number (GN) 43 flash. I'm trying to determine whether I should step up to something like the Strobist favorite Lumopro LP180 speedlight, which has a 110 GN. I had been assuming that I would have to jump to monolights, but according to Paul Buff's Expected Output even the stronger monolights are in the 100-GN range shooting through a diffuser like a softbox.
Am I thinking about this correctly? E.g., can I compete with sunlight using flashes? And is a 100-GN speedlight in the same class of output through a diffuser as a 600 Ws monolight?