There is this one, it seems a good compromise with 5cm of clearance, available for long travel model : http://byschulz.com/komponenten/sitzkomfort/parallel-gefederte-sattelstuetze-g2/
Julien,
I have not used the Schulz 'post, but a friend of mine in Germany purchased this seatpost and reports he has been very happy with it. No problems at all after a year of use.
I have not seen or used the Redshift seatpost, so I have no experience with it I can pass on to you.
One potential issue for non-Thudbuster parallelogram seatposts is whether the saddle rails will clear the linkages at the front through the whole range of available travel. I know some fitments of Brooks saddles on the SunTour seatpost result in an initial interference and "clicking" sound until the edge of the aluminum seatpost link wears(!) away. It seems this might initially limit travel as well. Our own Forum member StuntPilot has noticed this and so far as I know, remains very happy with his SunTour parallelogram suspension seatpost even after extensive use.
I do like the idea of adjustable springs, but I don't have personal experience with them.
I made (they are relatively easy to construct if you have machining tools) a telescopic suspension seatpost that has been in operation for my tandem stoker the last 15 years or so. She reports it is helpful and won't ride without it, but I do notice it has noticeably more "stiction" (sticky friction) than my parallelogram Thudbusters, so it hangs up a little at various points in its movement.
Have you made a choice yet? If so, I'd love to hear how you like your new suspension seatpost, Julien.
All the best,
Dan.