I'm not sure from your post whether your plans are to continue working solely with DV video or whether you have some plans in the future for HD formats.
In any case, I think that you would be much better served by making changes to both your hardware plans and workflow more along the lines of the following:
Single 128GB Samsung 840 Pro (don't get the std. 840, its writes are much slower) - OS/Programs; if you turn off the hibernate feature 128GB should provide plenty of space
Two 1TB 7200 rpm drives and either spread the load (projects and media on one and scratch / cache / outputs on the other) or RAID 0 them and put all files on the RAID array
Do nightly backups of media and project files to your DS111 (orgainze your directory structure so scratch, cache, and output files can be easily ignored from the backup)
This plan with give you way more speed and improved redundancy as well (as the DS111 is only a single drive unit).
With your new faster system you would probably enjoy using the local drives for photo editing work as well, especially if you go with the 2x RAID 0 array option.
Finally, you should probably increase the RAM of your new build to 32GB; what Windows 7/8 does not use for programs is does use for disk caching and that tends to speed things up for photo and video editing workflows.
A Gb connection has a theoretical bandwidth of 125 MB/s. In practice this comes down to around 65-70 MB/s, far slower than a single SATA disk, which has a practical bandwidth of around 150 MB/s. It works, but slowly as you already surmised. Why not add an internal SATA disk or even a couple of disks to your system and use the NAS for backup?
I plan to use HD video from a camcorder in future.
I want the material i produce to be available to other computers in the house. (I do this for hobby I should say). I would like to dig a bit deeper to the NAS performance issue to understand it better. After having imported videoclips (until now stored on the NAS) and saved my project on the NAS as well isn't it possible to put rendering results and preview files on local disks but keeping the raw data and produced video files on the NAS. In such a scenario would really the NAS be accessed during editing and adding of effects?
I have a similar specified PC to the one you are proposing to build, I also has a Synology NAS unit.
My 211 NAS is not up to heavy use as a source for the media, I use mine to store the completed movies and also it has a backup copy of all the media thus it is available for use on my other PC & laptop
With your PC spec I would go for a 225GB SSD boot disk and a seperate SATA 2Tb for media/preview/cache etc files. I can give you an idea of how quickly a media disc can fill up, I have over 200Gb of cache files alone on the disc.
You could also have an external e-SATA disc which could be moved from PC to PC
I am with Harm, regarding editing to/from a NAS. Even with a dual-Gigabit connection, I found it just too slow to be useful. I use mine for archiving source material, and just Copy any Assets to an internal HDD, for editing - the originals are untouched on the NAS. This was with SD material.
I found that FW-800 was the minimum, that I could live with.
Now, I have not tried my NAS to provide a streaming signal to other devices, as I have not had that need.
Thanks for all answers.
I thought that by setting scratch disks to a local drive would result in that videoclips that you have imported to project where put there as well.
I interpret your answers as that is not the case.
I think your suggestion to keep originals on the NAS and copy them temporarily to th local disk (be it a SSD or a "magnetic drive") would work.
The pictures I would use in videos however is more tricky since those are accessed/edited from other computers in the house.
Do you think that storing stills on NAS and accessing them from there (but keeping local copy of videoclips on local disk) would also slow down editing and rendering a lot (whatever that is)?
Would that make the investment in a fast CPU and Graphic card meaningless?