After much testing I've nailed down my TSE 2012 rig...(pitcured)
Starlapse, 500mm F4, 5dMkIII, Manfrotto 501
Rig is remarkably stable and fully balances out even with that behemoth Canon lens.....with zippo counterweights!
Still not sure whether to run the Canon at its native 500mm or use a 1.4x converter, but kudos to Canon. Even wide open (attached test pic) the lens is sharp as, with nil CA (note the lack of purple haze around the street lights )