How well does healing gear transform into spell power gear? I want to know if my priest would be better served by holding onto epic items with high healing stats or by blue items that are +damage for grinding in Northrend. For example. Would a pair of pants that are +90 to have higher or lower spellpower than a pair of pants with +40 damage?
It is not a direct one to one conversion and some of the changes may be surprising -- or at least they surprised me. Let's look at a couple of examples from the gear my Priest is wearing right now. My usual healing pants, Whitemend Pants, on the live realms, have +62 healing. On the Beta realms, the same Whitemend Pants have +33 spell power. Alternately, my DPS pants, Trial-Fire Trousers, have +49 damage and healing on the live realms. On the beta realms, the Trial-Fire Trousers have +49 spell power. I've seen a similar pattern across the board -- healing numbers significantly reduced, with spell damage numbers staying about the same. I'm sure it will work out fine in the long-run, but when you first enter Wrath, you may find that your DPS gear gives you more overall healing power than your healing gear!
As several commenters have noted, though your healing numbers drop, your actual healing ability does not. I personally feel my heals are hitting somewhat harder on the beta realms than on the live realms, despite a huge drop (really, massive -- my beta +heal number is sort of depressing) in the healing number on my character sheet.