Are there some good carbon arrows that are something like 450 spine?  I am finding I have a bow, that due to my draw length and arrow weight needs, just can't quite make it with 500/3555 spine arrows, and I am not all that happy with my heavy or real long 400/5575 arrows.  I would like to find something in the middle of the road if possible.  That or I need to start playing around with internal footing on a 500.

You could thicken your side plate just a smidge and shoot the .500's.  Thicken it a tad instead of a smidge and shoot even heavier points on .500's.

CE Heritage 150's at .487 are the closest to .450 I can think of.

You could also try 2018 aluminumn they are .464.

You may consider the Victory VForceHV 400's at 6.2 gpi (~$64/doz.)

Your finished arrow should weigh ~ 60 grains less than the GT 5575's.

Note: The Victory VForceHV 350's have performed quite well for me and readily accept a standard weighted insert.

CE heritage 150s are .487, and they do react a little stiffer than .500s, imo.

I was in the same boat as you not long ago.The only carbons i could find with a mid spine were target arrows.And they were about $150.00 a dozen.I ended up going with a plunger and a flipper rest.And tuning to what i had.I know thats not a option for everyone.But i really like it.

I may just try some aluminum shafts.  I just wish I could still walk into most archery shops and pick up a couple different aluminum shafts to try out.  I don't care for the CE 150.  I know all about the shimming of the side plate, but I find most of my bows at the weight I shoot would work well with an arrow between the 500 and 400 so would like to find a shaft that provides a better working range for me.  Thanks for all the input.

Try the PSE Radial weave 200s. They are a good tuff shaft and have a deflection of .424,or something close to that. Lancaster Archery sells em, 3 different straightness variations.