Well, I know I'm not really allowed to contribute, as I only have the chassis of an 851sp ... but ...
1) I don't find the steering at all 'flighty', and louigi has jacked it up too. It's more precise and gives more feel than an SS for instance, and certainly has more feel than a 748 with a 60-profile front.
2) Weight - remember that a lot of sp's have alloy tanks and special wheels - both of which show up on the scales and when riding - you''ll not believe how much better an alloy tank makes a bike feel as you're throwing it from side to side unless you've changed the tank yourself and felt the before and after. (the beast is of course so light it will make any real 851 feel lardy
)
ps
at the moment, I'm enjoying riding the beast more than the 748 (see other threads re 45mm pipes/cans) so may end up _having_ to change the 748 for a nice 851 strada in my search for the ultimate midrange grunter that doesnt throw your licence away