I'm basically of the mindset that shadow is one of the most subjective caster spec/classes to gear. This is especially true if you're never going to do arena as shadow.
Players rarely die 1v1 in BG's and no amount of resilience stacking is going to save you when you're locked up, silenced or ganged up on without a healer. I'm fully in awe of a Sunwell geared SP and the damage they can dish out. My shadow priest can't get Sunwell runs to save his poor Conqueror behind for me to say he's well geared for the spec but he's respectable.
I'm a big proponent of stacking tons of PVE gear on this class for BG's. Shadow simply has a ton of outs, dispersion, psychic scream, psychic horror, engineering belt, fade that resilience is not the deciding end all be all IMHO. As such I don't endorse the Chardev guide listed on this forum..... at all. Of course though that's why we're here, to agree to disagree.
I'd go with T6 bracers, belt, boots and possibly pants. I'm more partial to Pantaloons of Growing Strife than T6 pants but.... the 4 set T6 bonus is really nice for shadow. Given the 3 sec cooldown reduction on Psychic Scream with the PVP gloves I'd almost tell you not to take the Sunwell gloves. You can't make up for a reduced CD. All gear selections should really be made with how you know you play and also possibly situational on the BG and what the opponents and your team's class makeup is before you start the game.
My best advice is this.... gem/enchant all your PVE gear as you would if you were playing PVE. PVP gear the way you would PVP. Mix and match as your play style and BG's allow. After all, if you're going to be running with a pocket healer? You're going to want to pump out all the hate PVE gear can muster.
Despite what many opinion makers on here would have you believe we all know that we're doing 95% of our BG's in PUG's and frequently with/against players that are in ungemmed/unenchanted PVP gear or god forbid (If they're on your team.) or god willing (If they're on the other team.) BOA gear. Against players like that really don't know what they're doing? Stack that PVE gear all day long and love your screen shots with 30 KB's and 600k damage.
I'm fully convinced that only 20% of the people I run into in XP off BG's are true dedicated twinks as we would define them on this forum. The rest just turned off XP long enough to honor cap on their way to 85.