No prob, Jim. Here's why I think that. With Sumerian farmers, I can just build the farm and pretty much forget about it. But with Persia, I have to constantly think back and remember to use the bug. Yes, it's incredibly simple to do, but I do forget to use sometimes. I, personally, never use the bug in a game with APC'ers, but must admit using it when playing unknown's. Getting back to my reasoning for thinking it doesn't have much of an impact, I have several reasons.
You won't be farming until Bronze because of berries and elephants/gazelle. If it's a water map you won't be farming until Iron because of berries, elephants/gazelles, and both shore fish and fishing boats.
If you are farming before this I think the farm bug won't help you too much because your opponent is gathering food faster than you and can thus amass a larger army in Bronze to defeat you before Iron.
Ok, accepting that all I have stated is true, what about when you get to Iron Age and start using the bug. Well, I feel that once in Iron Age, each player is forced to micromanage 70+ vills/Fishing boats and at the same time field an army of no smaller than 25 units at all times while usually being much, much, much, much greater. Therefore, with Persian farmers, it is somewhat difficult to always check on your farms, espcially when playing 2.0 speed. I find myself constantly rebuilding even my Minoan farms which have a 25% increase in production. However, Sumerian farms produce so much food that you can simply sit back and relax and not have to worry about it, which free's you up to do complete other tasks, like reassigning your Fishing Boats...etc.
Fact: Persia is helped while Sumer is hurt by the farm bug.
My opinion: Not enough impact on the game to alter the end results.