For me personally, sPriest requires a lot of movement in arenas and battlegrounds. Using shifting requires you to stand in the power circle and what not, so really you would only get the passive haste.
I would say noise machine is probably your best option. Spriests are very squishy at around 30% resil, getting a little damage absorb wouldn't hurt. 54 intellect wouldn't hurt either.
Skull is probably my second choice. Haste on demand helps, although i wouldn't take it over noise machine.
Lightning Generator is semi-useful if you don't have tazik. The crit can help with mind blasts. I know personally that I will get 3k non-crit mind blasts and 9k crits. The extra 2k damage I wouldn't say is a huge factor.
That's my input at least. I'm not Mr. Spriest over here, but I think I know what I'm talking about
I hit about 2k running spriest/rogue. I would never suggest running spriest/healer in 2s, the damage isn't good enough in my opinion to take down a good healer. I would like to think spriest/mage or spriest/elemental would work, but i wouldn't know because my server has all of one other twink.
Cheers.