How much will 1" of feather effect arrow flight?  I've only used 5" shield cut feathers up to this point.  I've shot 4" feathers on carbon arrows from my compound with no problems using field points and broadheads.  But I don't think I've ever seen them used on cedar.

It depends on how good you tune and how good your form is.  A well tuned arrow shot with consistant form, does not need a 5" feather, even with a broadhead.

As lefty said, if your set up is tuned, then 4" is all you need, I shoot 4" shield and parabolic with 145 grain snuffer to no ill affects.

Also depends on the feather area - I can burn a pretty robust 4" feather that's fairly high at both the front and back, and probably equals the area of a typical 5" feather.

I chop my feathers with a 4" shield cut. I do not shoot wood any more but never had any problems with 4" on wood and I use to shoot them alot. You should not have any problems with 4" feathers shield or parabolic. I do chop my feathers hight profile.

Dido above. If not getting the flight ya want, try 4 fletch with 4" on a tapered shaft.

A 'robust' 4" feather in a four fletch configuration is typically more surface area than a 5.5" three fletch. I only use 4" four feather fletching.  :D

I like big 5.5" helical and then I don't have to worry if I have  perfect form ,which I don't, or if my bow is setup perfect probably not.
 What is hoped to be gained with the smaller feathers a little more speed?

I'm lucky enough to have arrows that fly almost dead on at 30 yards. I changed to 4 4in and love it. Seems to my eyes like there is less drag and that they shoot flatter.

If yer a feather chopper or burner, you'll get a two 4" fletches from one full size feather.

A 4" four fletch can give ya more surface area and no need to orient the nock and be cheaper in the long run.

Getting 2 out of 1 full length is what made me try them to start with.

I went to a 4" 4 fletch because I can get a complete arrow from 2 full length feathers instead of 3.I'm pretty sure I've got more surface area than 3 5" or even 5 1/2" useing the 4 but I would al;so suspect that just 3 4"ers would do just fine.I've not tried that from any of my sticks,worked no prob with the other thing I used a long time ago

Good luck