Dragonlee has a point in that Lee must take time to open the gates. Except the Gate of Opening. That alone makes his speed faster, and Lee can do that while running. He did that in his fight against Gaara in the Chunin Exams and Kimimaro while Naruto chased after Sasuke. Neji does have the 8 Trigrams Rotation but I don't think he'd be able to use it even if everything slowed down in his Trigrams because of Lee's immense speed. And while Neji can strike chakra points he would have to get very lucky to actually hit a successful blow on Lee. In the end I think Lee would win the fight.
Indeed Lee is extremely fast and strong, but also correct me if im wrong but Neji does have a higher level past 8 trigrams right? when he was fighting the spider member of the sound 4 and was rained on by spiders i coulda sworn he upped it to 16 and went even faster, allmost stopping his preception of time, making him what i would argue on the same speed level as Lee with an opened gate.
If they are both precessing on the exact same speed, it could possibly go either way, sence Neji has is chakra sealing and Lee has his superb taijutsu.
At the same speed it wouldnt take luck for Neji to seal or even mess up Lees chakra points, he only needs one point per arm to stop all use of that limb, trust me i know alot about pressure points.
Of coarse all of this does hinge on whos faster, if Lee is still even somewhat faster it would be in his favor, but Neji still has all of his movements in his vision. not limited by direction like the then underdeveloped sharingon of sasuke, the byakugon can keep up with Lees motions up to a point depending on how much faster Lee currently is. Sasuke couldnt keep up with Lees movements because not only it was not fully developed but also he has to actually move his eyes to look somewhere else, unlike byakugon that can look strait and see all around (minus the small blind spot)
I mention all this because when factoring the byakugon into the possible difference in speed, Neji can still see Lee even if he cant react fast enough. Lee moves in a form like motion as seen in his fight with Gaara, even if most didnt see it, but his moves are all rhythmic and to a point predictable when moving on instinct, which is the case when moving at such high speed, the faster you are the less you can controle, to a point that if seen, the moves can be predicted by Neji.
Also if i remember correctly, while i dont disagree that the first gate can possibly be opened while in motion, if memory serves (and its been a good while) Lee opened the first gate by using a lotus technique, secondary lotus if i remember. Not while running, after that the other gates were opened while stationary and forcing them open.
But thats just splitting hairs and has no real impact on the debate.
As much as i love Lee as a fellow martial artist and idealist, i just dont think Lee would win this fight givin his current level, and untill i see some huge breakthrough in his technique that makes his gates faster or a new better way to fight Neji i cant really think he would win.
Also all of the gate stuff is based on the fact that he would use it right away or that be his main plan.
Lee had sworn to never use his gates unless he was going to save some one or if his life depended on it, a sparring match hardly fits into the situation.
AND Lee had intended them to be his trump card, not his main stratagy. He said so himself that he never intended to use it unless he absolutely had to.
Im not sure what context it would truely take to get Lee to go so full all out on Neji that he would nearly kill himself using the gates, which is allmost allways the outcome of useing them, just to win.
Hopefully in the future we will see more of Lee and Neji to the effect of a new technique that would decide this matter more clearly.