E6 feats - which to use?

[Gnaritas]

I am planning on making an E6-campaign, but i have some questions regarding the feats.

1. Is there an official list? including capstone feats perhaps?
2. I am confused about the "extra spell known" feat. There seem to be several variants used, i have come upon:
A- You gain a spell known to a spell level at least one lower than the highest
B- You gain a spell known to any level you can cast
C- Some variant that lets you pick a 3rd level (if you are 6th caster level) or a 2nd+1st.

And each of those has a similar variant for additional spell slots.

For my campaign, i ban Wizards, and Druids and Clerics must use the Spontaneous Divine ACF.
Now my concern is, that getting a 3rd level spell known and a 3rd level spell slot for a feat each, will make the casters increase in power more than the Barbarian for example. Who may be able to pick a few strong feats, but they will run out. The casters seem to always have a good pick with these two feats.
On the other hand, not being able to get new 3rd level spells known seems to be very limited to them.
So are those feats (B and C) indeed powerful, or am i overly concerned? Or should i just go with variant A and not let them have B/C

I am trying to figure out a solution to this problem (or maybe i shouldn't consider this a problem at all....):
- A caster is not allowed to have more slots or spells known of a certain level than any level below it.
When using variant B, this would mean those feats have to be used for level 1 and level 2 spells fairly quick, before one can get back to level 3 spells. This would limit the average power of those feats. When using the stronger variant C, this would hardly be a downside at all.
- A caster can only use those feats every x feats
For example, they can be used every 3 epic feats (feats after level 6)

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While i am at it, i also wondered about (Improved) Toughness, which would give 6 HP to all characters, i wondered if Barbarians should be allowed to profit more from such a feat than a sorcerer.
I mean, a Barbarian could be at like 62 HP (CON 16), while a Sorcerer would be at something like half that. Which means the sorcerer would add 20% to its total HP, while the Barbarian would add 10%. Or is this not a fair comparison? I would be inclined to let the HP added be dependant on the HD of the character, for example 3+half HD, which would give the sorcerer 5 HP and the Barbarian 9 HP.
As i am typing it seems i am overly concerned about casters ;)

[Lapak]

It seems to me you eliminate basically all your concerns by not offering 'additional spell slot' feats. That brings caster epic feats line with martial ones, in that you are adding to the list of things you might do, but not adding the ability to do more of it. I've always seen the fact that spell slots remain as limited, precious resources to be one of the primary balancing factors in the E6 model.

This also mean that the Toughness issue (and relative melee-combat benefit on general) goes away. If the sorcerer never gets any more spell slots he may need to get into the fray more often - either early to preserve slots or late because he has run out. So letting a feat like Toughness do more to close the HP gap isn't a bad thing.

And casters are generally more capable of doing that in e6 - the absolute difference between physical combat capabilities is lessened by the cap as well, so you rarely hit the point where the barb can't miss but the sorcerer plinking with a crossbow needs a 20 to hit.