I know a lot of people say when using SoR to let it run its course before judging it. Though it depends on what talents and gear you have, I say experiment with the mob you are on and determine what is most effective as each mob is different.
For my situation, first I will say I don't have Reckoning yet but I do see a potential benefit to it....will have to see though. In the mean time here is what I have done.
I am a lot like you in that I am working on a protect build.
I have quite a bit of spirit through my gear and I regularly have blessing of wisdom on which makes my mana refresh quite high.
Having 5/5 in benediction is a huge help in saving MP. I also have 5/5 in intellect but really that is only of use in multi mob fights. Also 2/2 in Improved Judgement to provide quicker judgements.
When playing solo I always lead in with SoCr and judge it.
For the experiment part, test to see how many SoR judgements you can get off on a mob. If you are barely getting 2 off, or your 2nd judgement is with a sliver of health left, just judge SoR near the end. This is especially useful on mobs that run away. Judging SoR is extremely useful for that situation. You don't want the mob running while you are waiting for Judgement to refresh.
NOTE: A key to recasting SoR after judging it is to do it immediate after a swing so that you can recast SoR before your next swing. In my case, Judging SoR gets me close to 200 holy damage and a swing gets me about 60. If I don't recast my SoR before the next swing, I lose the Holy damage on that one effectively making my judgement only worth about 140.
As my note above aludes to, when grinding it is all about efficiency.
Personally with my setup, if I am judging mobs three times in a fight (1x SoCr and 2xSoR), I can usually get through about 10 before I have to do any sort of resting. And that is only if I am going non stop with little to no delay between mobs. Usually the travel time between mobs is enough to get my many up again. If you notice your mana getting low, reduce the number of judgements you are doing for a couple fights and your mana should recover.