I know we are all making assumptions here, none of us know exactly how the discussions went back in 2010 when they were making design changes to mirror 10/25 man raid content between boss mechanics, and item drops. But it seems to me that they wanted 10 man to be more viable, instead of just a catch-up in gear for people who are trying to get into 25man raiding. If I base my argument around that assumption, then the spirit of that design change and direction would be that the rate of acquisition between 10man and 25man should be the same.
But in practice, in the beginning of a new phase with the next set of raid content, 10 and 25 man loot acquisition rate will be closer, because the more of the loot that drops will be upgrades. 10man will be at a slight disadvantage here, because they have fewer classes that use a particular armor class. But this becomes more apparent later in the phase and before the next phase release. The rate of loot acquisition becomes more and more in favor of 25man since raiders are waiting for particular pieces to drop and more loot becomes disenchanted. A 25 man raid, because the larger number of drops, will have a higher chance of having the 1 or 2 items that a particular raider would need when everyone is approaching full phase BIS. I could plot this out on a graph, and we could see the curve difference between 10 and 25 man.
If you increase the loot drops for 10man by 1 or even a 50% chance of an additional drop. Then in the very beginning of a phase, 10man will be at an advantage for loot acquisition, but it will start to equalize the further along into the phase you get, so by around week 5 or week 6, the raid wide loot acquisition will be close to equal. By week 9 ( or so), 25man will again pull far ahead when people are nearing full BIS.
For Firelands specifically, I think I estimated a few months ago in the Cata Beta forums that it will take a 25man ~8 weeks to achieve their first Dragonwrath staff. While a 10man will likely take ~10-12 weeks. Again, assuming the original intent and spirit of the design change was to make 10 man comparable to 25man, then the items that drop for the quests would also need to be adjusted. They should be adjusted anyway for both 10m and 25m due to the shortened Phase3 timeline.