So what you're saying is 25/173366316979 *(round time in weighted shares + shelved shares from previous round)= payout for that block. As long as those shares in the entire pool don't out weigh the total amount of shares for the current round.
No, the payout for the block is always 25 BTC. They are paid out to the topmost 173366316979 shares in the stack ("shelf"). If this is an unlucky round (greater than 17.3 Billion shares accepted) then these will all be from the current round, and some shares from the current round will be shelved to hopefully be paid out later. If it is a lucky round, all shares from that round will be paid, and whatever shares are on the top of the stack will be paid out until a total of 17.3 Billions shares are paid out. These shares may be from the last unlucky round, or if there has been a run of good luck, you may have to go back several unlucky blocks.
Now in the case of shares from a previous round, those would apply in the case of a over 100% luck round, or is that a different scenario?
Yes.
So if we had a 440% luck round, you would be paid the shares you submitted that round plus round shares that are still on the shelf from say a 25% luck round, or what have you?
Yes.
So the benefits of having more hashes are obvious, but the longevity is where you can potentially be paid your fullest possible earnings?
No, not really. Longevity (or just sticking around for more than a couple of days) will reduce your variance, but Eligius is pool-hopping-neutral and will pay out your shares regardless of how long you stick around. If you are pool-hopping, and happen to mine for 6 hours with Eligius during a lucky streak, you could very well be paid out for 100% of shares. Or if you happen to mine for 6 unlucky hours, only 25% of your shares might be paid out immediately, while 50% more are paid out in the next 36 hours during a good run streak, while 25% might remain unpaid forever. Leaving you with only 75% of total shares paid.
While if you mine continuously with Eligius (i.e., weeks/months) then you will see these numbers converge towards the long-term payout rate which tends to around 97%, and is almost always between 95% and 99% unless the pool happened to have a severe bad luck streak which would drag you down a little more. But as always, the bad luck tends to be balanced out by good luck in the long run, but there's no way to predict it, as each block mined is an independent event and there is no way to say that the pool "deserves" or "is due for" a block after going 12 hours without one (see Gambler's Fallacy). So I would say, the longer you mine, the more likely you are to converge around 97% of shares paid. If you mine for a short time, you could see 100% paid or 50% paid. Just simple variance.
Note that in this whole discussion I am using "paid out" to mean "BTC credited to your account", not "entering the payout queue" or "actually seeing the BTC in your wallet". The payout queue is an entirely separate mechanism from CPPSRB, see the post in my sig.