sorry, 550EX not a good comparison. I meant to say that the Metz 60CT4 was about $1.2k new (or at least it used to be).
You can read up about this on the web... try photo.net
TAKE NOTE that GN is expressed as a function of focal-length. That's why when Canon says oh... our flash is GN55 ... consider that their measurement is for coverage of an 85mm lens. You need to read the effective GN for a 50mm lens @100ISO... this is the industry-standard. I think for a 550EX its about GN40 @50mm. Metz rates their GN in ISO/50mm lens/in metres. In the US, they rate it in feet... GN is also a ratio, something like aperture values. I don't have details on hand... read it up on the web..
but ah... when Metz says their 60CT4 is 60GN ... it is GN60 for a 50mm lens, or about 30% more powerful than a 550EX !
BTW, my principals are correct... but my numbers are a bit hazy now ... so pls do your own research.