1.6.2 Lag

Well I was pretty excited for the 1.6.2 update after I got back from holiday. But i was serverly dissapointed with the quality.I downloaded the 1.6.2 launcher and let it do its thing and I hit the play button. I was taken to the home screen so I thought I would play single player to try it out. I opened one of my worlds. I was confronted with the most lag I have ever seen in a game. To put it into perspective in 1.5.2 I averaged 60fps, and now in 1.6.2 i average 11fps! This is just rubbish! My computer has more than the system requirements and why should my computer lag that much when 1.5.2 dosent? Mojang better do something about this!