I really don't know how else to explain this. We're discussing pure damage output here hence the preference for STR Sword off hand, and in any situation where you want pure offensive power it's what you'll be using. This precluded alternate situations where things like Sanus Ensis would be preferable or the PDT sword.

Almace's ODD can not proc on WS's, it's melee damage only but it's proc rate is much higher then Xcal's 2.5. Req vs CDC is a very big "it depends" as RDM has crap attack compared to other DW jobs, mostly due to it not being able to have /WAR with DW. You never EVER want your cRatio to be under 1.0, that's the territory of absolute sh!t damage. Req's -20% attack penality pretty much guarantees that you'll be under 1.0 on anything more then 4~5 levels above you. At that point in time a crit is double damage (1.0 -> 2.0) and crits suddenly become very important to WS damage.

Messed up thing about Xcal's add damage is that it's pretty much equal to using enspell 1's on a Dual Wielding job. I don't know about the precedence of Enspell II vs Add effect, I've NEVER EVER heard about them being different then Enspell 1's and until I see evidence otherwise I'm assuming their the same. The attack on Xcal is really nice, but it doesn't make up for the damage lost. In either case you would be using STR sword off hand, I really can't see anywhere that 3% would do more for you then 27.5 attack and 2.7 fSTR as you can already cap gear haste.

I've been around and around this for a very long time and no matter what numbers you plug in STR Shikagar -> Eph Sword, on both RDM and BLU. It's really just an expensive glowing sword good only for town gear.