I know this is a little late to the party but I wanted to answer this for the sake of future people who are asking this same question.
The answer is that Pinnacle of Rage can deal a total of 12 damage. Your second example:
- Pinnacle of Rage deals 3 damage to each of two target creatures and Pinnacle of Rage deals 3 damage to each of two target players
- Pinnacle of Rage deals 3 damage to each of two target creatures or Pinnacle of Rage deals 3 damage to each of two target players
was (mostly) correct!
This is due to the use of "each of" in the card. (This is where English and grammar come in.)
**WARNING** It's about to get a bit technical.
Each is a determiner. It is used before a singular noun.
Each of is used before a pronoun or noun with a determiner. It is followed by a plural noun. The verb is singular but can be plural in an informal style.
So what does that mean? Let's simplify it by removing everything after "creatures"
Pinnacle of Rage deals 3 damage to each of two target creatures.
Pretty obvious that it means both creatures are taking 3 damage right?
Well next comes the modifying conjunctions "and/or."
This is where all the hubbub is coming from. We will be specifically taking a look at an example using "and" since it just so happens to prove the point.
Here are the objects of the sentence only using the conjunction "and":
"...two target creatures and players."
Now, we'll be substituting different definitions of the conjunction "and" to give the sentence some clarity.
- "...two target creatures plus players."
- "...two target creatures then players."
- "...two target creatures in addition to players."
It is clear that four targets are being mentioned here. Thus PoR deals, at most, 12 damage.
This brings us to our second half of the "/" equation: or
It's harder to do substitutions for "or" since... well... there really aren't any. We can, however, deal with the straight definitions and apply them to the scenario.
(used to connect words, phrases, or clauses representing alternatives): [creatures] or [players].
(used to connect alternative terms for the same thing): the [creature] or [player targets].
To sum all this up: PoR can deal either 6 or 12 damage respectively. You just have to choose either conjunction within the sentence and use it appropriately.
- Choose two creatures and two players (yourself included if you are playing 1v1) and deal 3 damage to each.
- Choose two target creatures and deal 3 damage each. -- first definition
- Choose two target players and deal 3 damage each. -- first definition
- Choose one creature and one player and deal 3 damage each. -- second definition
A SMALL ASIDE
When looking at the ruling, it states
"2/1/2014 You must choose two legal targets to cast Pinnacle of Rage."
This is because the text of the spell specifically says "two targets" and that condition must be met (at minimum) or not be able to cast it at all. It's similar to any other targeted ability/spell: you must meet the minimum requirement of the specified target(s) in order to cast it.
An example being that one can't use Flamecast Wheel's ability if there is no creature for it to target on the field.
A small but important detail but it makes sense too when you think about it. Why else would they give it an Uncommon rating if it was a 6 cost 6 damage to two creatures (or another player and yourself?) I mean seriously. That's just wrong. It's 6 damage or 12 and that's what gives it an uncommon rating.
EDIT: Fun fact - If you have any doubts, look at the MtG website on Pinnacle of Rage. The English version of it is 2/5 stars whereas every other language (French, Italian, German, Japanese) have it at 5 stars. If you also take the text from those different languages and put them in to translators, it becomes quite clear that that ambiguity doesn't exist.