I had 15/40 on mine when I bought it and after about 9 months or so I changed to a 42 rear.
The first thing you'll notice (as you pull away from your house - urban riding - is that there's a little more 'pull'. Then you'll notice that it revs higher for any given speed/gear. Once you're on the open road you'll notice the real difference - it'll be much more responsive and lighter at the front. Will it wheelie everywhere? I think that depends on the type of rider you are. If you're inclined to wheelie anyway, then yes, it will wheelie big time. If like me, you're more reserved and don't actually particularly like wheelies (but like the front being a bit flighty and love gassing it away from bends!) then I honestly don't think you'll have a problem keeping the front down, just be aware that it's more likely to wheelie than before.
Mind you, I haven't tried it on track yet...! :crazy