I didn't do any speed testing on my UFS install. I can see how speed would be hindered. For the uninitiated, the way UFS works is that it expects, does not attempt to fight, and handles fragmentation very well. Well, it doesn't break. The speed loss is real, even in theory. It's slowed down by the idea of fragmentation even if there isn't any. That way it's not slowed down if it's run on a drive that's 95% full. It also doesn't run faster on an empty drive.
FAT and HFS are lots faster and generally more fragile than UFS, NTFS, etc. So the idea of defragging a UFS drive is kinda funny, because the drive doesn't care if it's fragmented. It'd be like trying to keep your raincoat dry.