From what I am reading now Galactic Readiness does not determine the end game but the Effective Military Strength bar which you can see at a terminal in game.http://www.oxm.co.uk/39560/want-the-...tic-readiness/
'Once they're on board, races and factions contribute their warriors, fleets and so forth to your War Assets total, which in turn feeds into your Effective Military Strength
. The higher the EMS, the more likely you are to administer said jolly good stuffing.
"Focus on that bar," says Bioware's Jarett Lee (via Beefjack) "That is your indicator of how well you will do in the end-game." Your Galactic Readiness percentage greases the axles, but doesn't power the motor: it simply multiplies your EMS total, letting you short-cut the minimum number of War Assets required for victory. Get 100 per cent War Assets, and you needn't bother with multiplayer at all - especially as there are more War Assets available in the galaxy than are necessary for optimum campaign completion."
"In summary: "EMS = success. EMS can be maximized via collecting war assets alone, even if your Galactic Readiness is 50%." Phew."
""Effective Military Strength" is the statistic that determines a player's success during Mass Effect 3's end-game. Collecting "War Assets" during the single-player campaign boosts this rating. Furthermore, there are more assets that can be collected than are necessary, but a certain threshold must be reached to get the "best" ending.
"Galactic Readiness," on the other hand, isn't even impacted by the single-player campaign at all, but increasing the stat by playing multiplayer (or Infiltrator) will reduce the number of War Assets one needs to collect in the single-player campaign to be successful.
"If you play a lot of multiplayer, you will need less War Assets from single-player to fill up your [Effective Military Strength] bar (i.e. it will balance out the requirements to account for you playing in both modes)," senior marketing manager Jarrett Lee states.
In summary, "Effective Military Strength" is the stat that determines Mass Effect 3's end-game proceedings, and it's a stat that "can be maximized via collecting War Assets alone, even if your Galactic Readiness is 50%.""