Topband: Beverage length

[LY2KZ]

Hi guys,
I'm contemplating to build beverage pointing to W6-W7-VE7 for this 
season. If everything goes well I will not be limited in its length. 
Therefore question: what is best length to use? I have read some 
material on the web and still not sure how velocity factor will impact 
beverage performance. My available beverage height will be around 170cm 
or 5'6'.' Ground quality is average.
Been thinking about 320m or 1050ft length.
What do you think?

Thank you

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Vytenis ly5t @ly2w