I tried doing a little comparison on my spreadsheet, with changing out the atmas. (This is the updated version with crit dmg cap at +100%. Also fixed crit merits to 5%, which the downloadable version hasn't changed yet.)
There's a mix of middling gear, and I decided to go with a slightly more damage-focused setup rather than speed-focused setup for SA/TA. Solo SA/TA only, not stacked with WS. Standard XP-level target. Aggressive play.
Swap out GH for Sanguine Scythe.
So it does go up a slight bit. You lose the evasion and reduced TP given from the Agi on GH in exchange for the +HP on SS. Out of curiosity I looked at replacing Apoc with GH to get back the TP and evasion advantages.
In this case, a miniscule reduction in damage to gain back TP given and evasion, but losing auto-RR. Though the real surprise was that GH was performing on par with Apoc.
Going back and trying out atma from the ground up (single atma at a time):
The (relatively) low value on Apoc atma surprised me. However it does sort of make sense. The thf setup had 16%-19% TA (Epona, +2 head, and either Triplus or Twilight dagger) before adding Apoc. The marginal gain for Apoc atma is notably lower for thf than it is for other melee, and SA/TA also takes away some of the weight of triple attack in terms of overall melee damage.
So by exchanging Apoc for SS, you're removing a moderately good atma (instead of a great atma), and replacing it with one that on its own does decently well, but also lends itself towards enhancing the area that Apoc doesn't, SA/TA damage. In the end you end up with total DPS almost exactly the same, but better survivability (more HP, no change in TP given or evasion) and less TP feed (fewer, stronger hits).
In addition, the more over-TP rounds (the longer you hold TP between weaponskills), the more it favors RR+GH+SS over RR+GH+Apoc.
As an aside, this also pushes average solo SA/TAs up into the 1500+ range.
Also also: If you remove SA/TA damage (solo tanking an NM or farming sound-agro mobs or whatever), RR+GH+Apoc pulls ahead again in damage by a small bit (~3.5%).
Edited, May 11th 2011 11:34am by Kinematics