So there is a server that I play on that is still in 1.5.2 and will be for a while most likely. I wanted to play on it so I changed my version of MC in the magiclauncher from 1.6 to 1.5. The game runs perfectly with around 40 fps almost no lag in 1.6, but when I play 1.5 the game is in like slow motion. I hit f3 and it says i have about 25 fps but it takes about 2 seconds for me to move, swing or anything in game. Even the options menu is slow. I am on a mac 10.8.4 with all software updated. If anyone has any ideas please tell me.
1.5.2 on the new magic launcher slow(Mac)