When I copy files from one partition to another, or from one drive to another, the transfer rates hover around 5-8MB/sec which is kind of slow given that all my hard drives are SATA II. I have the same problem when copying either a single file or a group of files.
I’m running openSUSE 11.2 x64 here (KDE 4.3.5) with three SATA II hard drives that are all formatted with ext3. I have dropped to the CLI and used mv and cp instead - this seems to improve things but I shouldn’t have to do this.
The only issue I have in kde (dolphin) is over ssh. It is slow, compared to gnome, very slow.
But otherwise, as what you describe, it’s fine.
Seems a bit too slow when compared to explorer on Windows XP.
I did some more testing and the data transfer rate seems to vary a bit more now. I just wonder if this has something to do with the host controller driver and its implementation. I’ve had similar issues with USB 2.0 transfer rates as well where the speed would start off high than dwindle down to a near stop.
Yes, USB flash drives are not special either. Gnome gives me better performance.
Writing to and from ext3/ext4 should be good. Obviously you can’t write to ext3 from windows. And certainly Linux, in writing to FAT or NTFS, is different than if you were using windows.
Would converting my partitions to ext4 improve performance with file copying ?
I doubt it. 
i don’t use dolphin, but in regards of write speed, with reiser i had the worst results.
ext3/4 gave me the most.
But this was from harddrive to harddrive.
With ext3/4 i get about 20-50 MB/s, with reiser it was below the 30mb/s range.
Not sure why, but perhaps it has to do with big files versus small ones.
Is my observation valid?