I'm shooting GoldTip XT Hunter 5575's, and their spine is .400. The chart on the GoldTip website says that for my set-up, 70#+100 grain+28.5" arrow, the recommended spine is .340.
Two questions. First, is the .06 spine difference significant? Second, and this one will sound stupid, but I'll ask it anyway, is .340 stronger or weaker than .400? Am I over-spined, underspined, or am I okay?
I'm about to upgrade to a dozen Pro Hunters and I want to get this right.

Yes, the .06 spine deflection is quite a bit.

.340 is stronger than than .400

You are underspined by quite a bit. The GT 7595's are right up your alley with a .340 spine deflection.

Crap!!![:@]
That's what I was afraid of. Let me backtrack for a minute. If my arrow is underspined, I'm going to have major trouble getting broadheads to hit correctly, right? Also, could that .06 difference result in a visible "corkscrew"apprarance in arrow flight? If so, I now know what my problem is. Another problem is that even switching to blazer vanes to decrease weight, this new arrow is going to be about 50 grains heavier. I don't mind the extra weight, but I've got a lot of sighting in ahead of me.

What buckeye said. Also the 7595's will quiet the bow down. Yes you will have trouble getting you broadheads to hit when you are underspined.

FYI

Spineisthe measurement of deflection in inches of a 29" shaft supported at each end 28" apart. The deflection is measured by hanging a 1.94 pound weight from the middle of the shaft.

A .500 spine shaft deflected 5tenths of an inch.
A .400 spine shaft deflected4tenthsof an inch.
A .340 spine shaft deflected 34hundredthsof an inch.
ETC ETC.

do what i did. trim an inch and a half off and they should be spined OK. i shoot Epic 400s. 67 or 68lb draw(i dont remember lol) and 27inch epics...with a 28 inch draw. i hunted and shot 1000s of arrows like that..kinda scary with a prong rest. the and of the arrow JUST barely clears the prongs...it was the only way i could get my BHs to shoot. they were 29 to start. saved me money from buying new arrows...i need new ones now and will get the correct legnth and spine this time....you can sometimes get around spine problems by trimming arrows(if you have the room...) or by increasing or decreasing draw weight and head weight. all are cheaper than buying new arrows....unless you NEED new arrows..

50 grains seems like a lot. I would think the 7595's would ony be 1-1.5 grains per inch heavier.

And yes, that would for sure cause your arrows to barrel roll and fishtail.

Can't do that. My arrows are already cut to 28.5". Another inch and they'l pull off the rest.
You're right. The difference in the 5575's and the 7595's is only .7 grain per inch. That's only about 20 grains heavier. I was looking at the 7595 Pro Hunter Hardwoods HD. For some reason the website says they weigh 2.7 grains per inch more than the 5575's in black. I wonder why?

well looks like u'll be buyin arrows.. lol.

the camo arrows weigh more because of the camo coating/paint. look at all the diffrent black and camo shafts..the camo always seems to weigh more.

You could try dropping to a 75 gr head.
but your best bet is to buy new arrows