A 580 on a G does make a rather top heavy combination, however those of us who use that combination a lot, use other solutions. Simplest is an ST-E2, restricts you to only group A + B (e.g. left and right), but you can have multiple guns in each group and vary the ratio between the groups. Of course you can do all the fun stuff of having brollies, boxes, etc. Using a large EX gun is very easy, a simple flash bracket gets the weight off the top, I use the Custom Bracket Mini RC, but there are plenty of others, control is maintained with an off-camera cord. I can then use the full master facilities of pro gun (be it 550/580/580II - they all work the same!), that gives you access to all the groups, A, B and C.