I haven't read through everything yet, but the firs thing I noticed is you're calling out 2 saps with the speed and stalking special abilities.
However, speed will give you only 1 extra attack, it's basically like having haste. Having speed on both weapons is a waste.
Also, flat-footed only occurs on the first turn of combat before the enemy has acted (unless you have some other method of causing them to become flat-footed). Being invisible or being hidden doesn't cause flat-footed (though it does deny dex to AC). It's also worth noting that on your first attack, you break stealth or invisibility (if you have it) and your subsequent attacks are no longer sneak attacks. Unless you have some other way to cause denied dex/flat-footed (or flanking) you will only get sneak attack on one attack.
I don't have time to do the mathematical breakdown, but deadly sneak is a terrible talent that actually decreases your damage on average. Don't use it. Also, at level 13 your attack bonus is so incredibly terrible you will almost never hit anything. At level 13 your going to be fighting things with an average AC of 28. On your best attack you need to roll a 17 to hit. Meaning you only have a 20% chance to hit with your best attack.
It's also worth remembering that in the first round of combat, you're usually going to have to move to your enemy so you wont get to full attack them. You'll get one attack with sneak attack damage.
Also, you're calculating weapon costs wrong.
You need a +6 weapon on each hand, because you must first have a +1 before you can apply special abilities. You need a +1 stalking speed sap. Of course, you don't want speed on the second hand because it wont do you any good.
Also, you're using stalking wrong, or at least you appear to be using it wrong.
It adds a number of d6 equal to the rounds studied, up to the enhancement bonus of the weapon. With a +1 enhancement bonus only, you only get 1 bonus die max. Also, the damage only applies on the first successful attack with that weapon.
It's not clear exactly how you're calculating it, but it definitely looks like you're calculating it incorrectly to me.
Also, if the +1 stalking speed sap costs 72,000gp of your 140,000gp for a 13th level character.
Slightly more than half your wealth by level, something you're not supposed to do.
Table: Character Wealth by Level can also be used to budget gear for characters starting above 1st level, such as a new character created to replace a dead one. Characters should spend no more than half their total wealth on any single item. For a balanced approach, PCs that are built after 1st level should spend no more than 25% of their wealth on weapons, 25% on armor and protective devices, 25% on other magic items, 15% on disposable items like potions, scrolls, and wands, and 10% on ordinary gear and coins. Different character types might spend their wealth differently than these percentages suggest; for example, arcane casters might spend very little on weapons but a great deal more on other magic items and disposable items.
From your description i am unsure you handly the Surprise Rund correctly.
1st. Sneaky Rogue gets into position right behind victim. No combat yet, because Rogue is unnoticed.
2nd. Rogue starts Combat with a Surprise Round against the flat-footed victim. Due to surprise round, only 1 Move Action, or 1 Standart Action. No Full-Attack possible yet.
3rd. If victim is skill conscious you need to win Initiative against him to give him a full-attack and still catch him flat-footed. Once he got to act, flatfooted happy-sap-time is over.
Anyway, if you hit in these situations a Sap Master Rogue will deal MASSIVE amounts of damage. IF you hit. For your character your to-hit-bonus is terrible.
My advice would be to get some simple +5 Saps and a bigger DEX-booster item, which boosts to-hit indirectly, as well as other nice stuff. Also there is an Ioun Stone for 4k iirc that gives a +1 competence bonus to hit. And i'd stack up on Potions of Heroism. Its a great buff, comes with +2 morale on to-hit and can be drunk silently. The cost is very affordable at level 13.
With the massive amounts of surprise subdual damage you can deal, it is much more important to make sure you actually hit your enemies, instead of trying to get 2 or 4 more D6 to damage.
P.S.
Like CLaxon said Deadly Sneak & Powerful Sneak are trap options! The actual increase in average damage deal is tiny (yet positive). Add the -2 to-hit on top of this, and it becomes a net loss of expected damage! You are more dangerous and deadly NOT using it!
Claxon: I did calculate it on the first hit only (that's the added 10d6 near the end).
Also I stated that it was assuming Flat-footed opponent & full round action. Now I know these will most likely never occur.
However, even fixing the problem with my misunderstanding of Stalking, and ditching it, I'm still at the problem of 90d6 of sneak attack damage if all hit.
Now I realize the shortcomings of the build (trust me I know it can't hit the broad side of a barn). However "Hitting" something isn't my worry. The point was to MAX sneak damage and if I was maxing it correctly.Nicholas Storm:: There are a lot of feats to swap around with this build and that feat progression could be a possibility.
You were still wrong because you would only have 5 attacks, not 6.
As I mentioned, speed will only give you 1 extra attack total, not 1 per weapon.
So you're down even more damage.
You get 2 attacks for two weapon fighting, 4 with improved two weapon fighting. You don't qualify for Greater Two Weapon fighting yet. And speed or haste will add only 1 attack.
You will only have 5 attacks.
