If you're referring to the Gulfstream G4, it's now called the G500 by Gulfstream. This may help your search a bit if you tried one. The Gulfstream website only lists customer tailored "eyecatcher" numbers.......max alt. 51,000 feet/mach .885 etc. etc.   The stall on this airplane will vary with weight and temperature. It's much more entailed on a jet than it is on a small aircraft(the smaller a/c normally using a fixed number). Approx. speeds should be around 210 for flaps 8 and 180 for flaps 20.  I would guess around 110-120 for max. gross, standard temp. stall.   Just take the thing out and stall it and see what happens! If you're really hardcore about the airplane, go to Ebay and find a manual(probably $50-$200 US). That may be the only way to get numbers, especially the stall speed(which requires reference to a chart).

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Actually, we're both wrong. G4=G300 G4SP=G400  G5=G500 and G5SP=G550.   


        i think............       That's the best that I can determine from the website. Very nice site BTW if you're in the market.

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Then what's a G450