as Mr S says, I was this close (cut to forefinger and thumb less than 2mm apart) from having an 853 kit fitted to my 748.
But....for £2.5k (cost of all the work) I got a mint 916sps with 126bhp and 77lb torque
I guess the difference is that I had a fairly standard E model, no ohlins or bling to speak of. If I had all that on there, chances are I may have made a different decsion....but I glad I didnt, because it is no less fun (more so because of the awsome accelaration) and its lost almost no money from what I paid a year ago.
If you can afford to chuck £2.5k away on relase value, and your going to rag it everywhere, probably worth it. If not, spend the cash on a 996sps/R (depending on what yuors is worth) and swap any bits over which are not on the new bike.
just my view