Between the time of their fight during the Chunin exam arc and the SRA, Sasuke didn't get to much besides his third tome and his Curse Seal lvl 2 which means Sasuke still has nothing but Chidori that can get past Gaara's defense. Though with Gaara being able to flood the place which could overwhelm Sasuke along the starting distance being 25 meters, I don't think Sasuke is gonna be able to reach Gaara anytime soon so I'd give the win to Gaara.