Here's my subjective 2 pence on the subject:
I currently own an 8x8 9C, a 2805 9c, my mate owns a 9x7 9C, and I own a HS3540, and I have punished a previous 8x8 9C into a very early grave, the corpse is rotting in the corner next to the casting couch in my garage.
My HS3540 has caused me a lot of grief, what with side cover screws being so thickly epoxied in place that there is no screw face at all, and the axle has shredded to pieces two different torque arms, and I am now only happy with a combo of Kiwi's awesome Greyborg torque arm, coupled with double ebikes ca torque arms on the other side. I hate the axle on the HS to bits, it is as if it is made out of thin frozen diamond it is that slippery and sharp and torque arm destroying.
But having said all my gripes above with the HS, I would choose my HS3540 over any of my 9Cs in a heartbeat. For me that is three things, 1) it just feels and rides so much better than any of my 9Cs and is much quieter, 2) The watts I have thrown at my HS bone stock (no cooling holes, no upgraded phase wires, no mods at all), would have smoked my 9Cs long ago, in fact they did, running about 20% less watts when I sent my 8x8 9C blubbering sobbing and begging for its mamma into the grave. The heat dissapation is just so much better on my HS than on my 9Cs. I used to baby my 9Cs, but I treat my HS no different to my X5, and it has held up bone stock (having said that she gives off a terribly unpleasant smell from the places I take her to, and 3) the wheel build that came stock with my HS from Crystallite is awesome. The rim is a chunky welded rim, with 12 guage spokes. Whilst I have never broken a spoke on my 9Cs personally, my mate breaks his fortnightly, and mine are very worked indeed, and the wheel build on my 9cs is cheap rubbish. I realise you can build a motor into any wheel as you please, but both rims and spokes (on both my HS and my x5) were stock factory wheel builds, as were the wheel builds on my 9Cs, and you simply can't compare the two.
I realise that I just listed a bunch of serious grievances about my HS, and then pretty much only complained about my 9Cs wheel builds (which can be fixed), and their tendancy to crumple under abuse. But I hate to say it but I love my HS. As Chris Rock says, "You have not loved someone until you have thought about killing them! Until you have stared at that rat sack, and practiced your alibi.... you have not loved that person!".....
I love my HS..... my 9Cs are like those girls off backroomcastingcouch. I can't fault them but I.... just..... feel..... cold.......about them.....