Like every one said, it is not the tyres its the pressures and the suspension.
I had similar issues with my Base and I was thinking to my self all the time why on earth this thing is struggling to handle. I got to a point of waiting for an 899 instead thinking everything would be a lot more better.
However, few months down the line, I have managed to get an expert to set it up for me and boy oh boy the bike has changed massively, all the issues I used to have before has gone and the bike handles wonderfully. I still need to tweek the front a bit but other than that I can say I am not going to bother with an 899 now!
The rear can take the power now, the bike literally feels planted in fast corners with excellent feedback from front and rear and it does not do silly things like changing direction like a fruit fly and being unstable in fast corners and not feeling stable and planted. I am really happy with the change!
If any of you guys are having issues with their handling (on a Base) send me a PM and I will email you my settings which you can try and get back to me with feedback, would like to know if others get a similar feel. Obviously it is up to the rider and their style of riding but I would like to use their feed back to improve this setup further.
Cheers!