Lee and Neji are both taijutsu users. Taijutsu and speed correlate with each other. In order to beat someone in a taijutsu fight you have to be on par with their speed, as shown by Sasuke vs Lee. Neji also kept up with 0 Tail Naruto who blitzed 2 Toome Sasuke. So we atleast know that their speed is comparable definatly faster than 2 Toome Sasuke can see.
Do you seriously think that VotE Naruto is at the same level of Chunin exams Naruto?
Anyways, if Neji can see the way the chakra flows through Gaara's sand and thus hit it with his gentle fist... Gaara wins high diff (probably even needing Shukaku).
If Neji can't, Gaara wins low to mid diff, most likely low.