I believe rock lee without his weights is faster than neji, after all he was training exactly to beat neji, to achieve that he HAD to be faster.

even assuming that rock lee without his weights and neji would be on the same level of speed (after all he wished to defeat neji BY opening the gates, so it would mean that only with opened gates he would be faster than neji, but who knows... we don't know for sure) rock lee when was hitting gaara he didn't try to aim at anything, then imagine that neji would have to break through the sand shield, then he should be fast enough to aim and hit gaara's tenketsu and besides that we don't have anu guarantee that sand armor wouldn't save gaara.

if neji would try to do hakke 64 he would have to be super fast to breach the sand shield every time he try to hit tenketsu, but as we've seen sand shield can make a wall of sand and do not have to react at everytime it seems gaara would be hit (sigure the rain ninja, rain of needles... remember??) so we could safely assume that neji would have huge problems with hitting gaara's tenketsus but I must admit that wall of sand was seen only that one time, but with it gaara would be save.

I must admit that neji defense IS better than gaara's... BUT it depends.
Kaiten is better in defending at the exact time when neji could have been hit, it consumes a lot of chakra but neji isn't poor in chakra, but gaara's sand is the worst thing to neji's kaiten.
to avoid gaara's sand neji would have to do kaiten all the time, gaara could send sand in neji's direction all the time, some of the sand would be mirrored by kaiten and after the while it would be "operative" again (it's mirrored and then it can attack again), but there's some sand in that gourd... neji would be doing kaiten and sand would be coming and coming and coming... on contrary sand shield is done automatically and it would block most of neji's attacks...

I hope u understood my point:P