The 51 feels like an old "muscle car" compared to the CBR 1000RR/Fireblade, which feels like a "big brother" of my old CBR 600RR - (see sig).
While I don't have track experience (is that what you are looking for - RE "handling" feedback?) and don't own a '12 model Fireblade, I will say that the Fireblade feels easier to handle and feels lighter than the 51, mostly due to its weight IMHO. I don't know the exact wet weights for each off hand, but I'm sure you can Google it.
Love them both. Perhaps you can find a local rider with a '12 Fireblade and check it out in person or visit a dealership that will (not likely LOL) allow a demo/test ride. Keep reading reviews as well. It seems most of what I've read indicate it's still similar to the '08 - '11s, but the reviewers are raving about the updated suspension. Other than that, not much of an overall "redesign." Some like the new dash/tach, others not so much - probably a personal preference.
Looking for a used '08 - '11 will save you some coin, can't go wrong there - more money leftover for mods to get the bike setup just the way YOU want it.
FWIW - the '11 models came from the factory with ZERO recalls. Read the following very carefully (and it's not a knock against the '08-'11 lineup).
There was an "engine whine/abnormal crankshaft noise" tech alert for the '08 - '10 models - click me.
Also watch for engine oil consumption - click me.
Has been an issue on '08, '09, some '10s, and possibly '11s.
Haven't seen any oil issues with my '11 yet. Nor have I read about any actual bitching from '12 owners either. Not ALL of them suffer from oil consumption, monitor your oil level on a semi-regular basis and add as needed, especially if you run the engine hard in the upper RPMs quite frequently.
Take what you read online about the '08 - '11 models with a grain of salt and don't worry TOO much about all of the reported issues, monitor them, but don't "freak out."
FWIW I saw a local dealership post a pretty low price ($9499) for the new 2012 Fireblades. I'm sure their price doesn't include the typical "dealer fees" or sales tax (MI sales tax is 6%, which comes out to just a hair over $550 if taxing the $9499 price, making it a $10K bike out the door).
Keep in the mind that the dealer will probably add the usual "prep, assembly, etc" and other fees BEFORE they come to the final "taxable" sales price on the bike, so the final out-the-door price for a cash purchase would be closer to the $10,500 - $11,000 pricepoint (if not higher LOL). Still might be worth calling them to find out the real scoop if you are in the area or to use their price for comparison shopping purposes/dealership haggling:
Or, if you wait until later in the season you can probably find one for a low price in your neck of the woods or just wait it out until next year and buy one as a leftover model if you truly want "new" and don't want to purchase a used model.
YMMV & g'luck !