If the talent still works as it did a while ago, then Remorseless Attacks is pretty useless even on fights like you mentioned for the sole reason that it requires that you get the killing blow in order to activate. Obviously that can happen, but it's not very reliable. I'm guessing Deadly Momentum would act the same way. It's pretty much a solo-oriented talent.

To the people suggesting to spec 2/5 CttC, I think it's worth mentioning it looks as though you'll run into problems if you choose both Venemous Wounds and Murderous Intent at the cost of Cut to the Chase without subspeccing into combat for Imp. SnD. At 2/5 CttC you'll need an average 2.5 Envenoms to renew SnD. 3 Envenoms and 1 Rupture (to enable Venemous Wounds) requires just over 24 seconds of SnD time if current cycle lengths can be assumed to stay more or less the same in Cataclysm. This is problematic as unimproved SnD only last 21 seconds. It's probably possible to maintain the cycle sub 35% with Backstabs, but with only 2/5 CttC it looks as though the cycle will fall apart above 35% if you try to weave in Ruptures. The problem was previously adressed by Vulajin in the wotlk alpha when CttC only procced on crits - a behavior which isn't all that different from 2/5 or 3/5 CttC.
If nothing else it atleast supports the previously mentioned comments about CttC at 5 points for 100% is somewhat problematic - atleast aslong Venemous Wounds remains tied to a Rupture that doesn't refresh SnD through CttC.

With a 52/21/3 or 51/21/4 spec (one unused point to either spend in CttC or RS) one important consideration is keeping SnD up via <100% proc chance on CttC.

Assuming my math is correct and we can Envenom 3 times in a full duration Imp SnD:

Using the formula P=1-(0.x^4) where x = % chance of proc via CttC

With 2/5 CttC the probability of refreshing SnD via proc over this duration is: 78.4%
With 3/5 CttC the probability of refreshing SnD via proc over this duration is: 93.6%

There are a slew of other variables to consider, such as the possibility of using low CP Envenoms if SnD is below some threshold, at risk of falling off. Additionally the glyphs available to us may drastically change how we use rupture, if at all and the entire spec might look considerably different if the lower passive (poison/white hit) damage reduces our value of haste and makes Opportunity much more attractive. Obviously if you are going to be the rogue exposing your spec will look different.

In any event I think at this point defining the next rogue spec is a bit premature but what I'd like to see is some better math on the possibilities of <5 CttC. Particularly if anyone has math on how many ideal (4cp+) Envenoms we can land in an Imp SnD I'd appreciate it. My assumption above of 3 is purely intuition and has no real mathematical basis.

One thing to consider is the increased crit chance on Backstab (vs Mutilate) and how it affects our rotation. My feeling is that we can expect 2 Backstab's per Envenom nearly always giving us at least a 4 CP finisher with Ruthlessness often leading to 5 CP finishers.

With regards to Venomous Wounds, I'm pretty sure it'll be worth it. Why? Because Blizzard wants it to be. I think the safest thing we can do in looking at most incoming Cataclysm stuff is to presume that every single number is bogus, but that every meaningful new mechanic is going to be re-tuned to the point where it worthwhile, at least initially. Rupture was worth it throughout Ulduar, and a fair portion of ToC, as we recall.

Of all the specs, the Combat model looks closest to being the same. SS for CP, with two finishers, one which is a buff, the other which is just bigger damage to use when you don't have to worry about buff uptime. Mutilate looks redesigned as if Blizzard is trying to walk-back the fact that they had changed it to a one-finisher model in WotLK, and rather than eliminating CttC they want to reincorporate another finisher, and intend to do so with Venomous Wounds. SnD remaining automatic, they want to bring back the two-finisher model (one "uptime" finisher, one "damage" finisher when the uptime one is safe). This is clearly how they want Mutilate to look in the end.

However, that doesn't mean that VW doesn't look lackluster right now. It appears there is no way for a fixed damage proc to keep up. However, if the VW was rewritten "Your rupture ticks have a 15/30/45% chance to deal one-half (or one-third, or one-quarter, or whatever it takes to make it balanced) your Instant Poison's damage to the target," I highly doubt people would think of it as being quite as unsexy. We know how IP scales, but as written, we have no idea how VW would. At very least, it'd be easier to think about how it'd play out once this all goes live.

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As to lower numbers of points in CttC, it'd be possible to test some specs like it in live. Drop a few points from it and try it in place of a standard spec, while keeping fairly high rupture uptime. You wouldn't want to do it in a HM fight, but a 277t10 geared rogue doing it in something like a 10m alt run (ie: with raid buffs, fight mechanics like movement, and reasonably high boss health) would probably give a good impression of how such a spec would play. Something like this would probably be a good testing spec. It goes 3/5 Relentless Strikes, since that seems to be a number a fair number of people are suggesting might work given the current Cataclysm trees, as well as 2/2 Imp SnD - both to mimic theoretical Cataclysm specs, rather than provide top DPS. It isn't designed to be a good spec (it's clearly worse), just to give an experienced, tactile sense of playing with a smaller number of points in CttC.