Well, NFS uses UDP, and maybe you'ill need some extra coding to ensure that no files get lost. I don't like it and it's not fully supported on all OSes.
Maybe FTP is your answer for FAST reading, so FAST transferences since no software is faster than FTP to do so.
But you say that you have a total size of ~500GB. You can implement some VCS using checksums to know what files need to be updated, but it's more coding and there are lots of VCS's. However, I think FTP is the best way if you want portability, and maybe read access does not imply a copy of everything. Even this way, FTP is the fastest one.
So, if you want a VCS, to transfer just needed files, just fast. If you have Unix-like systems on all computers, you can install GIT, and use
git pull to update the repos. Nobody will be able to write to your repo, and just needed files will be updated, fast.