Topband: Top Loading wires

[Larry - K1UO]

Could someone tell me the length of top loading wires (4 wires planned) needed to add to the top of a base insulated 90 foot Rohn 25g tower to maximize the radiation resistance on 160 meters.  I understand there is a point of diminishing returns on the top loading lengths.  The 4 wire angles will be around 45 degrees or as close as possible.    If I knew how to model ,or even had a modeling program, I would attempt this already relatively simple task to many.  
>From 50+ years of practical experience, I am ‘guessing’ maybe 28 feet long each?