I use gerbv and have never had any issue with using it to view files over a network. Are any other network operations unusually slow too?
I recently replaced my old Qnap NAS with a new model because it was weirdly slow with anything that involved a lot of file accesses. Raw data throughput with big files was fine, but the number of discrete operations/sec was severely limited.
The latest versions of OrCad PCB were particularly badly affected. They'd load and save .brd files quickly enough, but trying to open a folder containing a large number of files (eg. my symbol library) could easily take a minute or so, populating the file browser a few file names at a time.