he didnt get faster with the curse seal lvl2, he really didnt he doesnt get any faster with the curse seal lvl 2 in the game either, it just increases his strength and chakra, and he has the ability to fly around, just think about it, moving at insane speeds with those "wings" isnt really aerodynamic is it? in this case ( SOZ DBZ REFERENCE ) he did it WRONG, he increases strength and endurance, but no speed gain, maybe a little, but not the speed gain he gets after he goes cs lvl1,
im not saying he gets slower after cs1 he just doesnt get that much faster, naruto also gained insane speed when he whent kyuubi 1, but it seemed more like his strength gained when he went kyuubi 2 ( it also seemed he got a little slower )
IMO cs lvl 1 sasuke has a better chance against neji, having the speed advantage and stuff

edit: if he got through ti "just fine" it shouldve torn of gaara's arm/shoulder off as well, it didnt, it lost speed on impact, losing lots of its cutting power