Topband: insulated vs:bare radial wires

[Jim Hoge]

Greetings,
 
Can I expect any noticable difference using an insulated wire for radials? Theoretically, the velocity factor of the insulation will make the physical length shorter but is a tuned 1/4 wave radial length that important when it is buried or laid on ground? The plan is to use 18ga awb, of which I have some 30k feet at my disposal. 
 
tnx,
Jim W5QM