I've been discussing this with a local friend, and we're a little fascinated by Sarkhan the Mad.  I'm going to make this mostly about the numbers.  Since his main draw to us is his ability to draw cards in R/B decks, we want to know what the average R/B deck will expect to get out of his "0" Loyalty ability.

Using the 1st place list from Kuala Lumpur, modified to fit in 3 Sarkhan the Mad:

4  Arid Mesa
4  Dragonskull Summit
4  Lavaclaw Reaches
8  Mountain
4  Scalding Tarn

3  Ball Lightning
4  Goblin Guide
4  Hell's Thunder
4  Hellspark Elemental

4  Blightning
3  Burst Lightning
3  Earthquake
4  Lightning Bolt
4  Searing Blaze
3 Sarkhan the Mad


I've cut the Quenchable Fires and 1 copy of Ball Lightning to give us max value on our Planeswalker's draw ability.  This may be a horrible cut, but we needed a theoretical deck list to work with, and I wanted to cut high CMC cards.  I'd rather have Hell's Thunder, since Unearthing it and then turning it into a Dragon is really unfair.  Additionally, Hell's Thunder is harder to kill in combat, ensuring it survives to turn into a Dragon.


Dragons are just the bonus with Sarkhan, anyway.  The fact that you can use Sarkhan to draw another one, then next turn make TWO dragons, seems quite good and quite deadly, but we're concerned with our Sarkhan EV today.  Let's take a look.  These are assuming a 60 card deck, obviously, so the numbers change with every draw step.  We can fine tune them later, but let's just try to put a baseline number on his draw power.

Now clearly you'll have 5 land out before then and have likely cast some spells, including your first Sarkhan.  Lets say we curve out nicely, hit our first 5 land drops, cast a 1 drop, 2 drop, 3 drop, and a Bolt, then a Sarkhan on Turn 5, on the play.  That leaves us with 49 cards in deck upon casting Sarkhan.


A bit of quick math shows us that more than 50% of our cards cost 1 mana or less (62% to be precise).  Over 75% cost 2 or less.  The odds of hitting a second Sarkhan should see it happen maybe once or twice in a PTQ length tournament.  We've got a 38% chance of scoring a freebie, a 24% chance of hitting a 1-drop, a 14% chance of hitting a 2-drop, 20% for a 3-drop, and 4% for a 5-drop.  That puts our average CMC in the above scenario - curving out and playing a turn 5 Sarkhan without missing a land drop, on the play, at at about 1.32.  If you do nothing but activate his primary ability, you will be able to activate him 5 or 6 times on average.  Even if you get the worst possible outcome, you'll get a 3-drop, then another Sarkhan.  He'll be a 2-for-1 anyway, find you gas, and replace himself. 


Clearly these percentages are not hard and fast numbers, but you get the idea.  It is almost impossible for him to get you fewer than 3 cards in this deck if left unmolested.  It's fine to make Dragons too, and to Lava Axe people, but tho
se require little math or thinking.  A slight wrist movement to turn the guys sideways is often sufficient.  


I wanted to show that Sarkhan the Mad is actually an elite card-drawing spell, albeit he requires the right deck.  He's such a prime piece of planeswalker because of his colors.  The bottom line is, he's a 5-drop in red/black that gives you a one-sided Howling Mine for at least 3-4 turns, if not much longer, and he can change gears to end games in a second.  I feel 3 is the right number for this style deck because of the reach it gives you in all dimensions.  Noteworthy is the fact that you will still get, on average 2-3 activations of Sarkhan the Mad if you decide you need a dragon right off the bat.

It seems that Sarkhan is great at generating card advantage.  If he only draws you a single card, he's likely either saved you damage or traded them down a removal spell like O-Ring or Maelstrom Pulse, which are normally the worst against you.  It's a 2-for-1 only on paper - it's really not much of a deal.  If you make a Dragon, they have to deal with the Dragon while Sarkhan draws you cards or lava axes them.   If they remove the Dragon and the Sarkhan on the subsequent turn, you got a true 2-for-1.  Remember, after making a Dragon, you can put Sarkhan to work on your library and expect to draw at least another 2 cards, quite possibly more, so it seems like making a Dragon is the best standby plan whenever your board allows it.  It's also OK to draw once and then untap, play or unearth a Lightning type creature, and turn THAT into a Dragon post-combat.  Unearthed Hellsparks and Hells Thunders love to turn into 5/5s.

If the Dragons start sticking, it's all over.  The reason Sarkhan the Mad is quite good is because a 5 mana personal Howling Mine is playable.  It's rare in Red-Black, who usually can turn cards into damage, so it gains even more value on its color combination.  The choice to turn Sarkhan into a giant evading beater, direct damage, or a Howling Mine means he gives the perennially linear Red Deck a single card that gives a wealth of options.  This level of power and this suite of options was dearly missing from Red decks.  Remember how good Sygg, River Cutthroat was in Jund because he let you just draw more utter gas?  It's a similar concept here.  His 5 cost is really pretty rough, but at 4 mana he'd be way overpowered.  You aim to hit 5 around the time you want to stop casting guys (or run out), which is why Hell's Thunder is exceptional.

Its possible that the metagame shifts in such a way that Sarkhan doesn't usually live to see full value, but as I see it, any turn they spend committed to killing the Planeswalker is a turn you have basically earned for free.  3RB sounds fine for a Time Walk to me.