I can't believe so many people test this stuff (I think korsovan got it closest?) and get it so wrong. Although it could be that since I'm playing on hexxit, the mod is somehow balanced differently, and I plan to test it (unless someone else running FTB can confirm my results.)
Anyway Bows:
If we're looking for max damage, but aren't concerned about rate of fire, then the only stat that matters is the fly speed. How can you test this? Make a bow with .2 fly speed(stone bound usually) .5 fly speed (paper) 1 fly speed (wood) and then 1.2 fly speed (slime or steel or a number of others)
Then use the exact same arrow shooting a mob without armor and compare results. You should notice the damage go up and it in no way correlates to the bow damage value (which I assume is there for whacking mobs with your bow.)
Now, of course rate of fire comes into play, and the a close second for me is durability so for me, the ONLY OPTION for a bow is a green slime bow which has 1.2, faster draw speed and great durability. The only modifiers I would consider are red stone and pistons. Also, I should note that once my pack gets updated and I can use flamestring, I absolutely will since it has the highest fly speed at 1.5 or something like that I believe I saw from an earlier post.
Arrows:
How hard is nether quartz to get? I mean really? I was running around for 1/2 an hour and had stacks of the stuff. You step foot in the nether and it's the 2nd most common thing behind netherrack. This, imo, is the only modifier you should be using! It adds crazy amounts of damage to your arrows! You can add it to a whole stack of arrows! What arrow should you be using? Well, for me, the slime bow shoots even the heaviest arrow, malyuhum(w/e) pretty damn far and pretty damn accurate. Enough so that if I was only using these arrows, I would be able to compensate pretty well. Here's the thing though, the modifiers add so much damage, and there's no durability, so you should actually be using a paper rod for the extra modifier! Please note, I don't have thaumcraft installed, so perhaps thaumium is lighter/more accurate. If it is, by all means use that instead. But please don't use cactus! I checked, jagged does nothing. I even went as far as trying to add durability to the arrows using diamonds and emeralds, and tried to give durability to the arrow by hitting mobs in melee with it. Guess what, arrows are unbreakable, even if you add durability to them. So jagged does NOTHING. Now, if you use a maly head and paper shaft, add two modifiers and load the arrow up with nether quartz, you get an arrow that shows an amazing 13-26 damage! I was criting mobs with no armor for over 50 damage on the regular using my slime bow! But, it gets even better. I can't believe I haven't seen anyone test paper arrows. That's right, PAPER! With a paper arrow, maxed out, you can get a crazy 12.5-25 damage on the arrows! From paper! On top of that you get a high 86 (88?) % accuracy, and one if the lightest arrows to boot! This is the clear winner for me since paper is obviously so easy to come by.
Fletching:
From my tests, doesn't matter. Anything other than feathers adds weight, but such a small amount it shouldn't make a difference. Even still, I go with feathers since they're the lightest, slime a close second and oak leaves are very easy to come by, so they're a good option as well.
Oh ya, you can also melee mobs with these arrows and do 25 damage to mobs without any armor and get the slight knock back effect of punching and same speed as punching. Love these arrows.
tldr; slime bow w/ flamestring if that's an option, otherwise enchanted(assuming it doesn't reduce arrow speed) string or regular and paper arrows with maxed nether quartz.
Also, sorry if people test and get very different results in FTB! I'll try to test later this week in FTB as well.
Thanks, and happy stabbing! 
Edit-
Was just looking at a spreadsheet that has most data values, and it looks like the enchanted string does reduce arrow speed, so don't use that. Also it looks like a thaumium arrow head has not base damage then paper and still allows for max modifiers, so I would use that for the head and paaper for the shaft if that's an option. However, this won't effect the total damage by too much (if at all) so it may be worth testing to see if you do in fact get more damage. Accuracy looks better though.
