I have been using .4s and .36s for awhile now. I see no huge difference in loss of distance. I do however, see a major increase in consistency. The bbs are less affected by the wind, and I get much better consistent shots. With your rifle shooting around 450, you should be fine using .4s. I like them more than my .36s.
As for your question about aeg barrels fitting, are you referring to compatibility with the stock bar 10 hop up chamber? If so, I do not think any will fit. This is based on the fact that hop up chamber upgrades like the aero chamber allow the use of aeg barrels. Thats part of the reason why people ditch the stock hop up unit. However, people here do not recommend the aero chamber, but what I am saying is just what I am basing my assumptions on.