Main/Cross Tension Differential

What's the biggest tension differential you guys have strung a hybrid at? At what point is the differential too much for the racquet to handle? I've heard 5 lbs is the most you'd want to have.

I've been tinkering with a gut/poly hybrid and would like the poly as low as possible and the gut as high as possible for longer playability but I don't wanna warp my frame or compromise its structural integrity in any way.

Someone chime in please.
 
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