I tried on a MacPro2,1 OSX 10.5.8 and there is no lag as you say.
However, there is a lag on my W7 64 Core2. It does not look a problem of spec, so the it might be a problem on Windows.
Can any windows user please check the patch?
The behaviour of ji.cellblock is very odd, as soon as the rows have different colors and they increase around 20, the lag is around 500 msec. if the rows are more than 40, then the lag doubles, and so on...