What we found is that performance definitely is improved and is most noticeable with a gigabit LAN connection. Figure 1 shows a comparison of RAID 5 Write performance. The biggest change is from the previously tested firmware's (2.0.3-0462) gigabit-connected results with no jumbo frames. All other results, previous firmware w/ 4k jumbo frames and DSM 2.0 firmware both with and without 4k jumbo frames, are similar.
Figure 1: RAID 5 Write Performance w/ gigabit LAN
Read results are a bit harder to sort out since it looks like the previous firmware 4k jumbo results have some anomalies. But, again the DSM 2.0 firmware doesn't show a significant performance boost with 4k jumbo frames enabled.
Figure 21: RAID 5 Read Performance w/ gigabit LAN
Since the DSM 2.0 firmware is a free download, there's nothing to lose by upgrading. And, it seems, a throughput boost to be gained. DSM 2.0 is available on all Synology products except for the DS-101g+, DS-101 and USB Station.
All NAS Chart data for the CS407 has been updated with the DSM 2.0-based results. So use the Charts to run your own comparisons.