First of all, Gaara's shukaku transformations should be restricted. Gaara can't control so it's not his power.
OT: Kakashi was fast enough to sucessfully use the Rakiri the only problem was that without the Sharingan he couldn't anticipate his opponents movements which is a problem when your fighting multiple enemies at once but Gaara is just one person, so we know Kakashi was at least as fast if not faster than Sasuke was when he fought Gaara. Which means he easily gets past the sand defense. I imagine the fight would end the exact same way Sasuke and Gaara's first fight did.
EDIT - This is talking about CE Gaara, SRA Gaara would stomp Kakashi.