Only advantage I can see is the 4lb being smaller diameter would get jigs down in deeper water fractionally quicker. I have used the 4,6, and 8lb Vanish and also same weights Seagar Red label extensively for jig fishing. Great, sensitive jig fishing line, only negative is it is a little harder to see above the water under some conditions. I don't like the 8lb version much with jigs below 1/4oz, it's stiffer and with a little memory and lighter jigs it won't really straighten out right if that makes sense. I really like the 6lb version of both brands with a Palomar knot but am pretty much fishing braid/fluoro leader with 1/4oz jigs on all my rods these days except for a couple with straight fluoro for the odd time I try lighter jigs. All I do is jig fish.

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