Had my 748s done about 2 years ago. Its a wicked conversion.
Sigma did the work. They did my mates 916 as well and I could keep with and most times leave his slightly on the road.
So worth it if you intend to keep the bike for a long period of time. Or its set up how you like it.
I have upgraded to a 996sps engine and bits at the moment but I am building the 853 into a track bike right now. Its simply too good an engine for me to let go.
DC.