I would think that due to questing likely giving us experience again (I assume regardless of difficulty) most will be heavily relying on building NV stacks up to a boss for a particular act. Each boss will likely reward considerably superior XP upon quest completion and with 5 NV stacks. Thus this will result in lots of new game's created while continuing to farm certain sections for the best XP/hour.

Given this I was wandering what many might consider an optimal route?

To start I believe Act I runs in the Cathedral up to the Skeleton King would perhaps be a great way to build stacks and to also get some decent xp from elites and champions up to the boss. The content is more tuned to Act IV in difficulty and should provide a much easier leveling path for Paragon levels. Yet, if inferno does reward XP, as I would assume it does with paragon in play, it will of course be the optimal difficulty to farm. This could perhaps be proven wrong, and it might be that Hell mode is far superior, but this is my initial assumption.

The first boss in Act II, Maghda, could also be a good boss to potentially farm for quest and experience with all the trash and elites and champions roaming about up to her. Regardless, the amount of xp per hour will be greatly boosted by quick kills and likely any movement and xp boosts that can be acquired with gear. Thus if higher Acts take way too long to complete various quests with I would steer clear as they are not worth the effort and will only slow you down. Unless you have amazing gear, are incredibly skilled, or have an excellent team to run with!

Movement speed will be incredibly important for efficiency as it will overall reduce running time. Any movement speed boosts will likely be required by teams to keep the boat moving as quickly as possible. Teams will perhaps be highly encouraged after the post 1.0.4 nerfs to monster health in groups being fixed to 75% max health increase. Lastly, the best weapons and increased resource regen and buffs will help to keep you dishing out damage as much as possible.

It is definitely all about speed, greasy speed! Not sure what the theorycrafters will recommend, but I look forward to see there breakdowns of average runtime for quest completion and boss kills, as well as xp per hour in each Act.