MDI Feature Pack Tab display speed

With the same logic, when I switch between old MDI and tab display, I observe a major speed performance.  In my sample test program, I created 25, 50, 75, &100 MDI windows.  As more MDI windows are created, the speed drop significantly.

FYI: My computer is I7 (3.4Ghz) with 24GB memory

Here is my statistic:

- 25 MDI windows, old MDI 0 seconds, tab 2 seconds

- 50 MDI windows, old MDI 1 seconds, tab 12 seconds

- 75 MDI windows, old MDI 1 seconds, tab 18 seconds

- 100 MDI windows, old MDI 1 seconds, tab 25 seconds