A few years ago I made a comprehensive study between the 900EX and the G-IVSP.
To make a long story short, I visited both factories, we took a number of demo flights in and out of Aspen, from OKC non-stop to London and back, to Bogotá and to islands in the Caribbean in both aircraft. I contacted some operators of both type aircraft to get realistic operating costs.
The end result was that we bought the 900EX, primary reasons were high and hot performance and the comfort of having three engines for the trans Pacific and Atlantic crossings. Around 20f and lower the Falcon 900EX can go from Aspen to London non-stop (with good VFR weather in England), the G-IVSP can not, no matter the temperature.
As for my personal feeling; I liked both aircraft very much, the 900 was nicer hand flying aircraft than the G-IVSP, but not enough to be factored into the decision of which aircraft to buy.
I'll try and find the report I summited to my boss and if I can find it I'll post it here, but in truth I believe it is long gone, along with 900EX when the boss got poor and he had to sell it and replace it with a Falcon 50EX.
In any case, I envy you, because doing such a study is a lot of fun. And do tour both factories, that was a blast.
So have fun and good luck.
