I am very keen that we allow CAP2 to play many roles viably. Otherwise, we miss out on exploring the full potential of Sketch. But to allow multiple roles, we cannot simply balance stats alone without regard to the move options, typing, and prevalence of attacking types, and their bias towards either end of the physical/special spectrum. Taking these into account, I feel that what reachzero posted earlier is a good way to go.
An explanation behind the reasoning follows.
First, a look at the weaknesses/resistances/immunities for CAP2
This also takes into account, roughly, the most prevalent attacking types (correct me if there are inconsistencies here).
Legend: Very common | common | noteworthy | rare | very rare
Weaknesses: Fire, Ice, Dark, Flying, Ghost
Neutral Types: Dragon, Rock, Steel (only 'common' because of highly prevalent Bullet Punch), Bug, Psychic, Poison
Resisted Types: Ground, Water, Electric, Grass
Immunities: Fighting, Normal
Now about the Stat Lmits
We'll assume that we will never intentionally take any SE hit (unless going for a kill) and will only switch into Neutral / NVE / Immune hits.
Physical Tankiness - Above Average
We do not need any defense to switch into Fighting moves, and Ground is the only resisted type that is dominantly physical. As discussed earlier, it's a good idea to allow things like Bullet Punch, Ice Shard, and Pursuit to deal good damage against CAP2, as it maintains balance. I do not foresee the need to ever stay in on or switch into powerful Outrages and Stone edges, which will anyway 2HKO unless we give it Hippowdon-esque defense, which is not the purpose here. Other than BP, we have Meteor Mash and Iron head for Steel, both from Pokemon which we have already predicted to be fairly good checks.
To top this all off, CAP2 has access to WoW (unless we break Type-move conventions), Cosmic Power, and Cotton Guard if it wants to go the defensive route. Given all this, a Physical Tankiness of Above Average should suffice. A Good or Very Good in this department will actually encourage CAP2 to sweep more rather than go defensive, since it will be able to slough off attempted revenge kills and checks with far too much ease.
Special Tankiness - Very Good
The bulk of CAP2's switch-ins are going to come from Water, Electric, and Grass attacks, all of which are primarily on the special side. On top of this, there are no special priority moves that are effective against CAP2, so revenge will not be attempted on this side of the spectrum so easily. Give it too little ST, and it becomes too much of a glass cannon. On top of this, support options go out the window.
Physical Sweepiness - Good
Let's face it. Its SE STAB coverage isn't very high and is resisted by quite a few common OU poke's. So unless we give CAP2 some coverage moves on its own, it will be forced to Sketch them. UnSTABbed moves will rarely make much of an impact unless they're backed up by a high enough PS.
But we need to keep in mind that Swords Dance (which is likely natural due to Type-move conventions), Gear Shift, Shell Smash, and Coil are extremely potent moves. Grass/Ghost has enough physical options that going with a "Very Good" PS will make its sweeping options too good. Good seems to strike the best balance.
Special Sweepiness - Above Average
The mere presence of Quiver Dance and Tail Glow warrant this. Grass and Ghost are stronger on the special side, and naturally lend themselves to boosting moves. Additionally, we need not worry about coverage here due to the presence of Hidden Power, which further warrants caution.
