Just build it: http://www.designer-han.nl/lego/8421xl.htm
Apart from the better outriggers of the 42009 this monster is the real big crane - at least IMHO ;-)
Mostly cause of the pneumatic (instead of the LAs), the smoother boom extension and the synchronized winch...
Well, it's more or less the 8421 but there are people out there who like it really big ... ;-)
BTW: just adding the double pneumatic stuff to the standard 8421 increases usability a lot because the boom can stay at top upper position very long (overnight in my case)...