And we use Xupload to monitor image upload progress which does not work on cluster storage (learnt this the hard way recently with Servage)
You may want to clarify this, a bit more.
Maybe it's the issue of file locking over NFS.
If so, there are other (and well known) ways of doing the same thing.
In other words, cluster storage (or "filer", "NAS", whatever they call) isn't really the issue if you know a bit of programming (or if you know someone who can identify and modify the code slightly).
Other than that, I don't know what was the problem with servage's storage.
I thought they had pretty normal NFS or something, and I had always coded with NFS compatible way that I never felt any differences.
(I used them a few years ago.)
These days, many hosts (especially competitive hosts) use NFS based storage,
and if the code isn't written for them, your choice can be limited.
But again, it depends on the real nature of the issue you had.
Even some VPS hosts can be using NFS storage.
Check about that if you are going to VPS.
About the mail, you can probably devide them and send them slowly in several separate batch.
Or maybe you can use separate list server, mailing only host/services, etc for that portion.