I saw a chart on a strobe website, can't remember where. (remember W.S. is a number left up for interpretation by every manufacturer, and to compare to G.N. is tough. With a reflector or bare bulb? What size and shape reflector? And on and on.) But this site rated this makers 250 W.S. strobe at 160 G.N. @/ISO 100. If memory serves, our SB-800's are G.N. 120.
The Metz 60 CT series has an output of 214 Ws (not watts per second, by the way). That's one of the most powerful portable flashguns around, apart from studio flashes used with batteries. Going by guide number at the equivalent angle of coverage, the SB-800 has less than half the output of that. The 60 CT-2 has a GN of 200 ft at ISO 100; the SB-800 has a GN of 125 ft @ ISO 100, both for coverage equivalent to 35 mm on full-frame.
I can't tell you exactly, but I use 800 Ws studio strobes (alienbees) for my main and fill lights, then I use SB-28's for hair and rim lights. I also use a 400Ws for backdrop light. They all mesh together pretty well, but obviously 1/2 power on my alienbees is much different then 1/2 on my speedlights. You just have to practice a little until you understand your equipment, then it's more natural. I don't know if I'd buy studio strobes that are 200Ws, unless they have a much higher effective Ws (which is common to see a 200Ws have an effective 600Ws).