I think the main issue with maxdps is that it doesn't take into account fight length at all, so it tends to go for haste as the best stat to get (to the point of suggesting all haste items for my balance druid that is currently at 600 +dmg).
Also I find it hard to balance upgrades, if you just go for the 'best' upgrade for each slot from maxdps then you'd probably end up with a set severely lacking in stamina and spell hit.
It's also not very smart sometimes. For example if you are say 17 points below the hit cap it would suggest something like
Hood of Hexing with 3x
Great Dawnstone. So your current helm would need 38 hit rating for that to be a logical upgrade (to not go over the cap).
Don't get me wrong, I think it's a good website and I really like the option to select upgrades from available instances, plus the handy item links so you can find out exactly where things drop from. But it's not a site you can just follow blindly and I find it less useful for planning entire gear overhauls (as you need to balance various stats in the process).
I've recently begun using
magegraf but I don't know how it compares in reliability to other spreadsheets.
Actually on topic, grats and I have no advice unfortunately. I tend to start the fight off with R1 frostbolt to stack WC if I think I'm going to have threat issues and then just stop casting or switch to AM if my threat is getting too high and it's too early to consider invisibility. Obviously though I'm at a stage in content where I can lower my dps for a portion of the fight without it leading to failure.