I think I will purchase a Giyua and do several Ghom DPS tests tonight, and see what I come up with.
A rule I try to follow with Spirit Barrage is 1 cast of Well of Souls and 6-8 seconds bears, and just keep movement up. Not sure if you noticed, but I used Barrage a lot more with wallers or reflect damage last night when we played together.
I've also considered using Haunt - Draining Spirit with the above method. http://us.battle.net/d3/en/calculator/witch-doctor#efUdXY!fcb!ccZYYc
With my CK (11 mps), SoS (13 mps), Haunt + ROE passive (25.3 mps), a Giyua (12-14 mps), and Zuni set bonus (20 mps), I would be at 81-83.3 mana/second.
Base mana regen is 20/sec.
Blood Ritual = 15% * 140 mana (Zombie Bears * 1.75 (Attack Speed using Giyua) is 36.75/sec (If I used mempo, it would be 39.4 mana/second, and mana expenditure would also increase)
Spiritual Attunement 994 base * 1.20 = 1192.8 *.01 = 11.9 mana/sec
Total: 150-152 mana/second. Not bad at all.
Mana spent per second: 245 at 1.75 aps, and 263 @ 1.876 aps
ACTUAL mana spent per second 245 - 152 = 93
I don't dare try to attempt the math behind using Mempo with Spirit Barrage Well of Souls. But I'm now very eager to get out of work and do some Ghom DPS tests to see which is better. I'll likely do 5 runs with Mempo, and 5 runs with a Giyua. Since this is single target, I might just forget Well of Souls, and use the Widowmakers with Vision Quest with Mempo.
1.75 APS might end up being a sweet spot in my gear.