Did my research and thought UNRAID was what I wanted. I was running a Mac Mini for Plex with Drobo connected as a storage pool and using my iMac for downloading torrents etc. Finally the Dynamic DNS client on the iMac allowed me to remotely access my downloads and add to them if need be.
I figured I would just build one UNRAID tower that could server Plex, download torrents that I could remotely access through DynDNS and have a bigger storage capacity than Drobo's 16GB. Along with that, I thought I'd probably be able to get better speed out of it as well.
Starting with speed, I'm getting pretty much a similar performance from UNRAID. Using my WD Raptor as Cache, I get about 45MB write speeds and about the same for reading. Speed wasn't really a concern for me in the first place but UNRAID didn't offer any improvement. With the latest firmware, Drobo now supports unto 24TB so storage issue is also sorted as I move to 3TB drives in the coming months. Haven't really had issues with protection either on the Drobo and it provides tolerance against two drive failures vs one on the UNRAID.
Applications is where I thought it would make a difference but it really hasn't. Plex works but it took a bit of configuration and with the latest update, I realized that you'll probably always get a newer version on Mac and PC before Linux. Also I'm uncomfortable upgrading Plex as my initial config took a while to sort out. Transmission on the Mac provides me with a script to unrar files automatically for convenience. Also, after a reboot, Transmission wouldn't start automatically on UNRAID. And finally DynDNS sent me a warning over and froze my free account saying I have started making too many requests and my alternative is to either pay $20 a year or switch to an official client- which obviously doesn't exist on UNRAID.
So I think I'll be heading back to Drobo. UNRAID is a pretty awesome solution but not for me. I travel for work once or twice every month and the wife and kids get very vocal when things don't work. While things can work on UNRAID, getting them to work without me being there is a lot harder than just telling them to reset the Mac