Title says it all. My stamina atm is 300 and I'm finding it ample to allow me to zoom in and slow time when I'm taking my shots and to run great distances on end, and also my carrying capacity is at a modest 500. So should I continue putting points into stamina, or just invest into health and a tiny bit of magicka now?

Note: I'm level 46 and have been using a 2:1 ratio for stamina:health until now. My magicka is also at 170 (I'm not a magic user, only ever used magic for restoration).

I go 2-1 also. Well I've been putting more in health lately cause they hit hard in master.

I stopped putting points into Stamina when I stopped running out of Stamina in Battles. But, I also don't loot as much as some do so I don't need carrying capacity.

Magicka - 100 (+50)
Stamina - 300
Health - the rest of the points

My archer dabbles in Conjuration, so I activated the Atronach Stone for additional magicka. With the perks it's enough for me, I might put some more points into it when I get Twin Souls if it turns out I need it.
300 Stamina is a comfortable amount. I rarely run out of it in battles (it's sneak-shots most of the time, so only a little loss when I'm zooming) and as carrying capacity goes, it's enough as well (combined with Extra Pockets perk).
The rest goes into pure survivability - health.

M-300 H-500 S-300 is my end preference for characters. So 300 is the stopping point.

I go 50/50 health and stamina because I never use magic aside from leveling to ridiculous levels, and for that I use enchanted gear to reduce the cost to 0. I have 460 stamina and by lvl 81 health and stamina are going to be matched at 500 apiece, currently lvl 73.

I stopped zooming because the accuracy while zooming is questionable and I hate having sneak attacks ruined because my arrow hit a few feet above the person I was aiming at. I just rest my crosshairs about halfway up the body and let the arrow fly, works every time.

My guy is pretty much exclusively an archer and I'm not really running out of stamina at 280 or so (lvl 61). I have a ring of regeneration 50% (found, not crafted) and the light armor perk. The only time I run out of stamina is when I'm messing around with sword/sheild or dual daggers. Since my dude has focused on the bow I think it's fitting that melee tuckers him out.

At long range I aim for the belly button and close up I aim for the collarbone. Both put the arrow in the throat. Eagle eye plus the 50% slow time is fantastic. I can burst into a room and put 6+ guys down before Janessa can get in my way.

It does not seem like you need to zoom that much. I can usually hit targets from far enough away even without it. My archer only seems to use Stamina when she needs to run away from something.