My current character started off as one where I wanted to test out the new arc values. I've always liked that spell and it turns out I really like it now that they scaled up how many times it can chain as it level. I ended up going in a different direction with that character and tried out being really tanky. It's fine, but it doesn't do any damage at all. But I do feel like arc can do damage if I spec properly for it, so I want to start again.
I also noticed while looking up the cost of all the challenge uniques that one of the three really expensive items would be really good for arc. I have enough currency to buy a copy of it, and I'm going to need a copy of it eventually, so it feels like I should buy one and then use it. It's a good theory but having spent the last few days browsing the item listings trying to buy one I've come to realize that there's a really big price difference between versions of the item that rolled well and versions that didn't.
The item in question is pledge of hands and it only really has two things on it that can vary. It can have between 120% to 160% increased spell damage and it can have a varying number of linked sockets. As far as I can tell you're probably going to end up at around 420-460 increased damage with arc so the difference between a top roll pledge and a bottom roll pledge is a ~8% damage boost. That's pretty significant. But how much is it worth? There is a currency item (divine orb) that can be used to reroll all random stats on an item so it's probably worth considering the cost of those when considering how bad a low roll pledge would be. You expect to get a 4% damage boost by using one divine orb, or a 6% boost from two... You can get unlucky here and use a ton of divine orbs and keep getting low results but it's pretty reasonable to assume that if you're willing to use 10 of them that you'll end up with a pretty high roll pledge. (You'd be 94% to hit at least one result in the top quarter of possible results.)
Unfortunately divine orbs are not cheap. They're about half of an exalted orb and if you consider the price range on pledges seems to go from 7-10 exalteds it's actually a pretty big jump to expect to use 10 of the things. On the other hand divine orb is one of the currency items you need to use in the challenge so the plan of buying a min roll pledge on the cheap and throwing a divine orb at it isn't the worst thing I've ever heard. And even with a min roll pledge I'm not losing all that much. I like doing 8% more damage but I don't know that I'm good enough at the game to really notice that loss.
The other factor is the number of links on the item. Adding an extra link to your spell is going to add a lot more than 8% more damage! Lightning penetration, for example, will be anything from a 34% damage boost to a 136% damage boost based on the resistance of the enemy you're fighting. I'd much rather have a min damage roll and an extra link! It's also reasonable to work out the cost of an extra link. Vorici will 6 socket an item for 150 jewelers and 6 link it for 1500 fusers. He'll 5 socket an item for 70 jewelers and 5 link it for 150 fusers. He'll 4 socket an item for 10 jewelers and 4 link it for 5 fusers. When you're talking about prices in terms of exalteds the 4 link is essentially free, the 5 link is worth between 2 and 3 exalteds and the 6 link is more than 20 exalteds.
I don't have 20 extra exalteds to throw at this particular problem and even if I did I wouldn't want to. If I did buy a 1 socket pledge I probably wouldn't even use Vorici. I'd throw a bunch of jewelers and fusers at the problem and be thrilled if I hit a 5 link but reasonably settle for a 4 link. But looking at the prices of all these orbs I suspect I'd probably blindly throw a couple exalted worth of orbs at it without realizing what I was doing. I probably have 3 exalteds worth of jewelers and fusers on me, which is actually a little surprising. I guess picking up all those 6 socket items does pay off!
But what this is telling me is that it's absolutely worth paying an extra exalted if it gets me a 5 linked pledge. Paying extra for a 4 link on the other hand is silly because that's easy to settle on.
Before looking at things I had every intention of paying 6 exalteds for any pledge I could find or 7 on one with a decent spell damage roll. But now I think I should be looking at paying up to 8 on a 5 link with a good roll, or 7 on a 5 link with a bad roll and just toss a divine at it. Is that viable?
The answer, at least for those listed right now, is no. A 5 link is more like 9-12 exalteds. I tried messaging some people who didn't have buyouts listed but none of them were willing to sell a 5 link for 8.
And then as I was looking someone put one up for 6 exalteds. 139% spell damage so right in the middle and not worth throwing a divine on. 4 sockets, 4 links, so no pressing need to throw any money at that issue either. Especially now that I've looked at it and got an idea for how much it costs to throw as many jewelers and fusers at the problem! So I think I'm just happy as is.