well, I haven't had to solo farm for awhile, but my spec doesn't have fel concentration either, so if I use the succubus it's because I have someone else to tag along (which obviously isn't solo farming). I'm SL/shadowburn/imp. lifetap. so a DSed voidwalker is basically infinite mana while soloing, where SL really isn't worth using for me. in pvp I use the felhunter most of the time, but if a match is heavy on melee I use the vw (succubus is too easily trinketed out of, and I have enough +damage gear to take down any class but warriors while tanking them, especially with SL). and when I solo, it's basically curse of elements, immolate, and then searing pain until it's dead - with all the damage gear I have, I get basically 2x the damage on searing pain, and it's not going to get interrupted as much. so the abyss shard would fit my playstyle a lot. it would also work well if I was MD/Ruin.
and on a side note, MAF, if you think raiding is lame, just wait until you try to pass rank 8 or 9 in pvp. at least with raiding you can clear something out in ~3-4 hours (which doesn't even have to be done all at once) and get drops that are just as good, if not better, than the pvp rewards. even if you like pvp (which I do), pveing is way better for gearing up for pvp if you're basically any class but a druid/priest. Let's say you clear MC 5 times and you get an upgrade in a different slot each time (a fair assumption if you're still in blues/greens). That's about 15-20 hours of work over 5 weeks, and gives you a big advantage over someone who pvps the same amount over 5 weeks. pvp rewards just flat out don't scale well - it's all top-heavy, and getting to the top requires so much constant playing and honor grinding that it will really burn you out.
I'm not saying "why pvp?" but rather "why pvp for the rewards?" Do it for fun instead, and don't focus on rank. I love to pvp, but I'm never going to focus on hitting HWL until they fix the broken honor farming system. also, the warlord's sets suck for the caster classes - you'll get way better pvp effectiveness by getting full felheart, and I'm not joking. I can only think of maybe 2 classes where their warlord's/marshal's sets are better than raided gear for dps - warriors and rogues - and I'm not even so sure about the rogue set (just that their set bonuses seem more useful than nightslayer at least, and I'd rather compare them to tier 1 because tier 2 raid sets are in another class by themselves). but, at least you can get a really cheap, cool epic mount by hitting rank 11. I know if I grinded enough to hit that on my warlock, I'd buy the black war wolf right away.