Other dilutions of DD-X and Rapid fixer

I would like to develop my first 4x5 and 5x7 sheet films. The tray is large enough for four 5x7 sheets. I already made a solution to separate them in the tray to make it easier to handle them. I cut a cooling rack and tie them with cable ties. As the tray is quite big I need a lot of liquid.
I have some Rodinal and DD-X at home. With Rodinal it’s really not a big deal to stay on the economic side but I don't know how far can I go with DD-X.
So I'm wondering about the outcome if I would dilute DD-X and Rapid fixer and instead of 1:4 I’d go with 1:8.
Has anyone experienced with this?
If yes, should I only adjust the time and if yes how much?
How it would affect the negative in any way?

If you look at developer time overview for DD-X on Massive Dev Chart, you will see several established developer times for DD-X 1+9, and the rare entry beyond 1+9. Forum member David Lyga discovered an interesting and very simple approach to use C-41 color developer in high dilution: just add Sodium Carbonate (washing soda)! If DD-X in high dilution becomes too slow, a small spoonful of washing soda added to your developer might speed it up.

For DDX, try diluting 1+7. Multiply the developing times you would use for the standard 1+4 dilution by 1.5 to get the developing times for the 1+7 dilution. So, if the normal developing time is 6 minutes, you would do 6x1.5 = 9 minutes for the 1+7 dilution.

DD-X at 1+7 should work well. The 1+4 dilutions of these types of developers can be a bit strong for many films.

Thanks everyone! I appreciate it!
I’ll go with your recommendations!