Firewire slower than USB on my drobo?

I've noticed that when my drobo is plugged into my Macbook Pro, via FW, it would feel slower than USB. To prove this once and for all, I ran Xbench and I came with these results:
http://grab.by/285w
And I'm wondering if its my drobo, or macbook or is this just the maximum that my drobo can output/input?
For bigger files, FW is faster, but smaller files, USB is faster...

Tech specs:
MacBookPro5,5
2.6 GHz Core 2 Duo
8 GB of RAM
500 GB internal, dual booting with Windows 7 64 Bit

Drobo specs:
4 Western Digital Enterprise grade hard drives (RE4-GP) 2 GB each, 3 partitions at 2 gb each. Partition tested was HFS+.

Or am I just being crazy/paranoid?

PS: for both tests, the USB and FW was plugged directly into the macbook pro and I am using the stock USB and FW cables

Not really all that surprising using 4k/256k blocks actually.... try using 2mb blocks and see what you get as a result.

Is there another benchmarking tool you would recommend? because I don't think xbench gives me an option as to what sized blocks I should test with.

I think SiSoftware SANDRA has a test which goes from 2kb to 16mb, but not sure. Check out what a few review sites use.