What length would balance out a 4000 size shimano reel? and what power would you get?

There are too many variables for anyone to answer this for you. The best thing you can do is take the reel with you and mount it on rods you're interested in. Power depends on what you'll be doing with the rod. In general a 7' Med/Fast is a good spinning rod for bass. A 4000 size reel is a little overkill and could be used on a MH or even Hvy rod if need be.

Just staying within the Shimano line up just about every 4000 reel has a different weight to it, the balance will be different with each on the same rod. Also every different type of lure will have a different weight too, affecting the balance. In one of my more anal moments I weighed each and every spoon, not every 1/2 oz. were exactly 1/2 ounce. same goes for other sizes as well. I'm not one to need a perfect balance, as long as it feels ok, I'm fine with it.

The weight of the lure is not part of the rod/reel balancing equation. The lure weight is what you are using the balanced rod to feel for.

oe

The weight of the lure is not part of the rod/reel balancing equation. The lure weight is what you are using the balanced rod to feel for.

oe

That's quite true.......

But changing the lure type will affect the overall balance, if perfection is the goal only 1 lure should be used, zero it to that one. Not that I buy into that.