After some pylon testing on my Staff/SR, I've found an attack chain with Guarded Spin + Fury of the Gladiator -Res proc outputs higher DPS than the chain I mentioned above. So does having Mercurial Blow -res for that matter.
All pylon times are with T4 Musc/T3 Degen/T4 Hybrid Core passive. Leadership Assault on. My only epic power pool is Physical Perfection from Weapon Mastery.
Serpent's Reach-Precise Strike-Assassin's-Sky Splitter
2:53
3:13 - sloppy start
-Didn't record further than this because I wasn't impressed with the DPS in a few half runs
Guarded Spin-Precise Strike-Assassin's Staff-Sky Splitter / Guarded Spin with -Res + 4 damage procs (98% dmg enh value)
2:55
2:42
2:47
2:20
2:31
2:32
Mercurial Blow-Serpent's Reach-Assassin's Staff-Sky Splitter / Mercurial with -Res + 4 damage procs (110% dmg enh value)
2:48
2:32
2:52
2:34
Guarded vs Mercurial seem close enough when comparing DPS, however the GS attack chain offers two added benefits:
1. Perma +DEF buffs from GS since it's now part of the main attack chain.
2. More Build Up reset procs on average in non-pylon content since the idea is you'll be hitting more enemies with a GS built in to your chain.