Shiva.Moogleking said:
Basic rule of thumb is if the mob is resisting your enfebbles then you need to increase enfeebling magic and magic accuracy. If mob is not resisting then you increase mnd and int for max duration and potency. Mnd for white magic enfeebles, slow, para, silence and addle and the rest are Int black magic enfeebles such as sleep, bind, gravity and so on. Unless the mob is immune then you shouldnt have problems landing anything with the proper set up. Good luck.
When I played RDM seriously (pre-Abyssea), my rule of thumb was that if I got resisted in full potency gear, I just recast the spell in full potency gear until it landed. If you get resisted on a capped RDM, assume that you just barely got resisted- especially now with lvl 90 skill (I almost never get resisted on my WHM or BLM with full Potency sets). The recast on these spells isn't very long, especially if you've Composure-Hasted yourself. The extra potency of the debuff will almost always be worth it in a fight where the mob will last the duration of the debuff (which are the only mobs people are likely to bring a RDM to anyway).
That being said, their MIGHT be some mobs out there that still resist even a RDM a fair amount, but I must assume that they are few and far between. I wouldn't carry extra Enfeebling+ and M.ACC gear unless you know you're going to be fighting these mobs. If you absolutely must have an Accuracy set, piece it together with stuff that you're already gonna have on you from other sets.