[50mhz] 5 over 5 stacking recommendations

[WD0T]

Greetings all, first time posting here! 

I have a question on recommended stack spacing, for using 2 cushcraft 5 element 6m yagis, looking to put 2 up on a short crank up tower for the June VHF contest.  By short tower I mean a 30ft to the lower 6m antenna. I am talking about stacking one above the other. 

What would you recommend for stack spacing using 2 of the CC 5 element, stock standard yagis?  Max gain would be nice, but also I need to not get crazy in terms of spacing distance.  I have seen in some places recommendations for .6 wavelength spacing for lower sidelobes, however I have also read that each type of antenna and height needs to be modeled to arrive at optimum spacing.  

Any help, thoughts certainly appreciated.  Thanks so much.

73 God Bless! Todd WD0T
DN94, Pierre SD.