this.gridControl1.AllowSelection &= ~GridSelectionFlags.AlphaBlend;
to turn off the alphablending and just have the grid invert teh cells to display the selections. Now depending upon the colors you are using, you will likely not be able to use this technique as teh inverting mainly makes teh selections black. But it should point out whether the delay is due to QueryCellInfo or the the alphablending.