Performance with the 6TB drives seems to be pretty good. Small, compact, and quiet.
Looks a bit better than the R6, but that's a personal preference.
Both are HW RAID. Both are Thunderbolt2.
There are a few reviews out there with benchmarks with the LaCie a bit faster with it's 6TB drives.
I like my 5big for the smaller footprint and quieter chassis.
Pegasus was first out the chute but I think LaCie did a bit better in the looks department.
I evaluated the Pegasus a while back but kept the LaCie.