So I've tuned plenty of arrows using this method, works wonderfully.

http://www.acsbows.com/bareshaftplaning.html

I shooting a 49lb at 26.5" longbow cut an 1/8" shy of center. Last year I bought axis 400 and they where to stiff so I bought 500's. With 325gr up front I got great arrow flight.

I wanted to try a different arrow this year so grabbed a dozen of the GT 600 blems from big jims. I put the same 325gr up front and wouldn't you know it they flew amazing!!

So why would I get such great fight out of axis 500 and GT 600 the only difference I can tell is the 600's are about an 1" shorter than the axis. Does the difference in diameter from the axis (9/32) and GT (5/16) pushed further from center make that big of a difference?

The diameter difference apparently does make that big a difference.  Actually, given that the .600s are an inch shorter, it doesn't take much else to bring them in line, but the increased diameter does help.

You don't have an anomaly.  The result you got is the result I would expect.

Plus the fact that the last batch of gt trads .600 I spined came in heavier then they were supposed to.

Plus you said the 600s were an inch shorter. Length makes a huge difference with carbons, so you have smaller diameter - closer to center and shorter length. Makes perfect sense to me.

Thanks guys, I guess I just assumed there would be a fairly sizable difference between 500's and 600's but that difference was negated pretty quickly but the diameter difference and that inch difference.
I've only ever shot 500's so thought I'd be cutting a few inches off of these 600's oh well quick tone I guess hahaha  

that difference was negated pretty quickly but the diameter difference and that inch difference.

Yep. I have one bow that likes axis 400 spine and 350 widowmakers(super skinny), same point weight.

how did you tune those gery?

Bare shaft planing of course. They are tuned to shoot with a fixed crawl. They are not the same length.