Upload & Sell: On
Guess it really comes down to what are you attempting to do with the Drobo. I have a S & a 5D. TB on the 5D is significantly faster as tested with different files size copy times. At the end of the day I use the 5D for movie, music and photo storage. It's never been an issue including running plex on the iMac that utilizes the 5D stored movies to serve up to my living rm AV system. I use the S as a pure backup via time machine. It's connected via usb2. For me, speed is unimportant for this duty. NOTE: you can get a eSata to usb3 converter for the S, hook it up to the iMac's usb3 port and the speed is significantly better. I got one and sure enough data flows faster.
Another point, if your drobo is >80% full it will start to slow down, natural condition.