One thing to consider is most people who run aeg tends to run it on auto and with midcaps if not high cap mags (6-12 seems to be the common range on your loadout) When you see GBBR folks, they tend to run semi auto ONLY and with real-low cap and a load out of 4-8 mags.
AEG: 8X 120 = 960bbs on full auto... 900-1500rpm
GBB: 6X 40 = 240bbs on semi auto (full auto max out approximately 1000rpm)
What's my point? GBBR folks use less bb in general, this mean that heavier weight is typically used instead. I've seen people running 0.40g on standard ( 400fps w/ 0.2g) GBBR.