Yesterday i decided to do some experimenting with different weight broadheads and had some interesting findings. My arrow/bow setup is tuned for 300 grain tips. I was bored and decided to see how it would do with some of the lighter heads i have because i have a bunch in the 125-200 grain range that would be just fine for groundhogs. Well with 300,200,175,150 and 125 grain broadheads they all hit with the corresponding weight field points at 20 yards. The all grouped nicely left and right, just hit higher as the weights went down. I was really expecting to get left/right variations on where they hit but none did. The 125's were the only ones that seemed touchy, a bad release seemed to show more but the others all did very well.has anybody else expirienced this?

You might be sliding on the strike plate just right to make good flight. Try a hard canted shot like your are leaning around a tree. You might find the arrows with light point weight slap the side of your bow or fly erratically. With carbon length of arrow is a more critical change than point wight. Most could get away with going up or down 50-100 gr in a pinch.

Im starting to think maybe i was leaning more on the weak side of spine. Just did some bareshaft instead of paper and holy smokes were my arrows showing weak with the 300 grain points. Shot some bareshaft with some arrows of the same spine that are 2" shorter with the same weight tips and they did great even at 20 yards.

If your bow is centershot or cut to center, as long as you have sufficient spine, you can overspine almost infinitely.  Going to progressively lighter points has the effect of increasing spine.  Long story short, I'm not at all surprised by your results.  Have been doing that for 30 years. Your really heavy points likely did make for underpinned arrows to begin with, as you note.

Im shooting a great northern shadow recurve and crooked stic hyperstic longbow. Neither of which is cut to center or past center

That is a little more surprising. Though I have found that I can overspine most bows some, even those cut proud of center.  Can just overspine centershot and cut to center bows a lot more.

There probably is one optimal arrow length,weight, spine, etc. arrow for a given bow at a given draw length and weight, but most of us aren't good enough to find it.  Luckily, we don't have to because most bows will shoot a range of spines quite well.

The more i tinkered around with the shorter arrows of the same spine and 300 grain tips today the more i think they are spining out pretty close to perfect for my 55# great northern but a bit stiff out of the 50# hyperstic due to being able to hear shelf contact during the shot. The other arrows which are longer are bareshafting weak out of both bows with 300 grain tips. So the big question is would i be better off using 300 grain tips and cutting them till they are good with the hyperstic and only slightly weak with the shadow or set up 6 with one weight head for the hyperstic anf 6 with a slightly lighter head for the shadow.

Either would likely work. It's your call/preference.  Ease with which you can keep track of which is which might be the deciding factor.

With 300 grains up front, you probably have an arrow in the 600 grain plus range.  That's about 12 gpp, quite a bit for a mild rd bow like a Great Northern, or is the GN a Ghost?  I'm not familiar with the design of your other bow.

Regardless, you might consider dropping 25 or more grains from points on the longer arrows and they'll probably shoot well out of each bow, and you'll still have plenty of arrow weight for most critters.

The great northern is a shadow, its basically the super ghost under a different name from what ive been told