I have learned that a 5D, battery, CF card and "nifty 50" lens together weigh about 1.3kg. Photohigher, for example, say their AV200 gimbal weighs 590g. All together that's 2kg. Going only by the numbers, that's well below the DJI's published payload of 2.5kg. However, I don't know what DJI consider payload. For all we know, they consider the battery and controller payload. And, obviously, this allows little room to add FPV gear.
Nigel, the 550D body alone is 530g. The weight of the 5D battery, which is different from the 550D but similar in size, is 75g. If you used the Nifty 50 lens (130g) your total weight would be around 735g.