For the most part I'm in agreement with the previous posts. I think hoppedup has a good point in that you might be better off with a taller stand rather than try to use an extension on the top of a shorter one. The manufacturers have certain specs in mind when they design a stand (generally, height vs. footprint) and when you add an extension to the top you're doing something that wasn't intended, it throws that balance out of whack, and you likely have a higher probability of the rig tipping over. It doesn't mean that it will tip over but when you have ~7.5 feet and throw another 2.5 to 3 feet on top of that without increasing the footprint of the stand, it's not quite as stable and also not meant to carry as much weight. And I think he's right in that ~7.5 feet is the bare minimum that you would need or want unless you're running head-height FOB. BTW, I think air cushioning is a nice feature as I've sometimes unintentionally let risers slip and it's jarring to have your gear come crashing down rather than ease down on the cushioning.
As also noted, the Manfrotto 099B is a great and versatile extension but it's minimum length is nearly 3 feet which could be a touch too long for the task at hand. That's what's nice about the 122B when you require something shorter. You can also connect the 099 and 012B (the 122 with a detachable base) together to make a pretty neat FOB stand but it's not terribly sturdy.
As far as the Manfrotto vs. Impact debate, I own pieces from both manufacturers and they will both do a fine job. That said, if I were to do it over again, I'd pay the extra money for all Manfrotto hardware due to the better build quality and design. The only place where I've found it doesn't matter a whit is in the Super Clamps: build quality is virtually the same for both manufacturers, IMHO. And it's also a good idea to have a Windtech C-clamp or two handy for those times where the Super Clamp is too heavy or you need a different solution.
As a final note, if you're doing any kind of clamping where your mics and gear will be hanging off into the abyss, safety cables are an absolute must. They're inexpensive and you'll look like someone who knows what he's doing as the venue's manager looks nervously on while you're manipulating your rig in thin air over the patron's heads. The likelihood that you'll have something fall due to your negligence or the failure of a piece of gear is pretty small, but why take the chance when a well-placed $5 piece of wire and metal can help avoid a catastrophic event like destroyed gear or, much worse, injury to an innocent bystander below? Better safe than sorry.