The bike is very torquey. Run it about 3g's on the tach, then give the throttle a good twist and it's like getting shot out of a cannon with the front forks wobbling at each gear change, because they're barely touching the ground.
The bike is definitely heavier than the SV650, but the trade-off being the bike is very stable even at low speeds (can easily get a knee down at only 25mph, and it self rights with ease).
I'm 5'5" at 135lbs, and the suspension seems to be just right, and the rear shock is a bit stiff, but that's how I like it; nose down tail up in the twisties.
I've replaced the air box with 2 K&N 40mm pod filters on 2 molded rubber hoses, and ran them slightly out of the forward fairing holes (created a short RAM for a carburated bike) I.E one short ram per carb ran out the fairings on the same side as the carb. Bike required a Stage 3 re-jetting due to all the air being shoved down the carbs. Also has a Scorpion stainless oval slip on. AiS has also been blocked off to stop the engine from sucking in hot exhaust gases.
Bike was recently dynoed on a dyno jet from our local race teams HQ Speedwerks in DE. They specialize in Ducati and SV650 race bikes and manage to squeeze out 89.5 HP on a stock block GT650R. The little bike freaking roars and walks the dog VS. a CBR600rr from a stop. Upgrading to stainless steel braided lines and EBC HH's all around.
Summarizing the bike is a great platform, great engine with a mediocre suspension, and poor but easily upgraded brakes. If Brembo made a retrofitted brake calliper kit for the bike, I bet they would fly off the shelves, and the Hyo will build up a lot of cred for being a good bike.
The bike handles well, even with its heavy weight. It needs a little bit of effort for the turn in, but the extra weight keeps it planted to the ground reaching max lean angle with no complaints at speeds nearing 50-65 mph on tight cornered back roads. And on the track requires a noticeable tug on the handle bars, coupled with body movement to turn the Hyo, but in the turn the bike keeps its line like it's on rails.
The engine has been very good engine that has soaked up a lot of abuse on track days and random bouts of hooliganism on public roads (not stunting, but a lot of hauling ass and knee dragging).
The GT650R could definitely be put on a diet; light weight wheels would drop the weight to a comparable size with the SV650. Maybe later drop the heavy steel trellis for an aluminum frame. Or make a trellis on par with Ducati (since their benchmark is Ducati, so why not?).
The fairings could be updated to fit flush with the frame for a more Ducatiesque look. Would also help in the fit and finish department, which is a weak area for the Hyo's. Some apparently having rust problems, and the really cheap looking plastic surround on the LCD dash could be replaced with a better LCD gauge cluster and a more form fitting plastic or a carbon fibre look dash.
I saw on the 2009 models they updated the triple tree from the "Silver Brick" of the older models to a much slimmer triple tree, much like that of the "Big 4".
Great all around bike for the price with potential to become a super sport bike when tuned properly, or when Hyosung decides to hook the bike bike up with some serious quality parts (Ohlins cartridge forks/Rear shock, Brembo brakes,). Drop the bike's rather porky weight to around 395lbs dry and you'll have a winner.