Yes the R6 does have less power at lower RPMs than other bikes. But, that's because it has so much power in the upper RPMs and screams to higher rpms than most bikes. Also, this is all relative. The magazines have to say something is bad. Mid range torque is the R6's weakness, plain and simple. However, the tradeoff is chip-controlled throttle, absolute screaming power in the upper rpms, slipper clutch, etc etc. It's up to you to decide what you want.
I can't think of any street riding situation where you would NEED to get on the power so hard and so fast that you would need to drop gears. But if you want to get on it hard, drop a gear or two. No big deal. I would say unless you are riding in a manner as to try and conserve gas (i.e. top gear under 60mph), you won't be disappointed. Yamaha made the gear ratios very close to eachother... the gears are very tall and only a couple thousand rpm in between each at most.
Also, don't forget that this bike was built to rev. There is no reason to keep it at rpms that you would keep another bike in. Cruising around at 8krpm is perfectly normal. Don't feel like 4-7krpm is the 'normal' cruising rpm... this bike redlines at 17500 indicated (16500 actual) And yes, the power does kick in harder at 10k (hold on!), but it's all relative.
You don't have to downshift to 'have power on the street'. The bike has plenty of power at all rpms and all gears for street riding. If you are riding hard on the street, keep the rpms up. No biggie.
On the track, you need to be in lower gears. Except for the main straight (up into fourth), I spent the whole track in mostly first and second gear, with a couple spots where I jump into third for a bit.
1st gear redline 80mph
2nd gear redline 100mph
3rd gear redline 125ish
4th gear redline 145ish i think
5th gear redline 155ish
top speed 165ish
Compared to your 250, you will chit your pants the first time you wind it out through the first two gears. If you are disappointed, I will eat my hat.
EDIT: If you are this concerned about midrange torque, maybe consider a more standard type bike like a sv650 or something... or maybe even the R6S, which is the old R6.
Dont worry man the new generation of R6 is a great bike. It FALLS into the corners something that takes alittle getting used to. I never had any problem at all with cruising around. Rember the bike mags have to be pickey as hell to compare all the 600's because of how close they are in performance. Little things that an everyday rider of the bike will never really notice they exagerate to make the bikes seem more indivual from each other