I have found, with a similar setup, the most effective to be as follows:


<----MAIN TOON---><-SUB1->
<-SUB2-><-SUB3-><-SUB4->

The main toon image takes up 2/3 width and 1/2 height of the screen. All the subscreens are pretty much square and take up 1/3 width and 1/2 height of the screen.

I used to stretch across the top like you, and also tried as per zanthor's suggestion, but with 1 screen I think this is best.