FWIW my ReadyNAS Pro is still beating every NAS out there...
...even with only 4 drives installed (RAID6 or X-RAID2, not sure which one - first can be recovered in any PC, latter is proprietary.)
But there is another side of the story: a HUGE PROBLEM with ReadyNAS is their uber-shitty, PoS proprietary OS support.
Awful-looking, long-outdated (my first ReadyNAS unit came with EXACTLY the same GUI in 2005!!!), inconvenient, counter-intuitive web GUI aside (I use it as a NAS, I don't go there too often) it's the OS/SW quality that sucks. It's basically one half-clueless (arrogant) clown rolling his own Debian-based (Debian!!!) pile of junk for *YEARS* now (seems he sold the company to Netgear but apparently retained the development of 'his' OS), producing one bugfest release after the other, unable to provide a f'n OS update without (re-)introducing another show-stopping bug for (literally) years now...
...it is truly painful to watch how an otherwise well-performing platform is suffering from more and more problems due to the mis-management/incompetence/negligence of Netgear, the lack of funds to bring in more, competent soiftware engineers, the grip of the clueless original developer/founder or rather the combination of all these issues.
In short I think performance/speed is one thing, having proper support and a developer team who knows his mojo is another and both are equally important - I never used Drobo but I bet it comes with less glaring CIFS problems, does not sport disappearing or randomly renamed shares, mysteriously shitty transfer speeds, they don't tell you to start tweaking your Windows' MTU size, to get a different brand of jumbo frame-enabled switch in order to utilize JF etc etc.