Anybody know how my ride will improve in the rough water with extension boxes?

One of the best things about having extension boxes is that you can run 380 tabs instead of 280s. With the drives farther back you just need to trim a very small part of the corner of the tab off to turn.
Doing this to my 382 really improved the ride in rough water and helped pick up a little speed.

neutral or 3 inch negagive?

Hi Dave, sorry I haven't gotten back to you. Not sure if I understand the question. If you are asking how I run my tabs to get a little extra speed, I run them down just a touch to lighten the back end a little. ( In calm water of course ) As you know there is no set place to have them, all depends on the water. But anyway with the bigger tabs you can pick up the back a touch with less drag than the small tabs because they are on less of an angle.
It was nice talking to you a few weeks ago, hope all is well.

Bought my 353 with boxes. Would like to know what difference the boxes make. Takes some finese to get on plane without blowing props out. I am running 525's with stellings boxes, xr drives, and 30 pitch 5 blade maximus props. Keep us posted as to performance improvements if you add boxes.

There is a sweet spot, a very small one at that. I feel your pain, I have the same issue. Sent my props to B-Blades and waiting to try them out.

I'll let u guys know what happens. I hope to hit the water come June

All that is good BUT if you use Stellings boxes you lose the drive coupler....That means get out your checkbook for more drive issues. Bad Idea.

I have imco neutral boxes

From what I was told the fastechs that came with boxes from the factory had a 1" higher x dimension