I converted my 748 SPS to an 853 - well I actually bought a brand new 853 engine - and did another 10,000 miles b4 the big-end bearing failed!!!
The bike was however, awesome, well able to keep up with a 996 in a straight line - no worries.
The grunt was amazing - from 3,000 rpm all the way to the redline - no hesitation - no spluttering just smooth power all the way.
I now have a 999s (05) which is also awesome.
Go for the conversion - you will love it.
Khushy