2) why aren't you using NEWSEQUENTIALID??
I don't know why OP doesn't, but me...
I don't use it because it's useless! It does not guarantee sequential order after reboot as it's just a simple wrapper around UuidCreateSequential WinAPI which never had order guarantee...
BTW, I try not to use GUID's at all, however sometimes it's unavoidable. The company I'm consulting right now had bought into 3-rd party product which has CLUSTERED GUID's PKS in all tables.
So, I enjoy looking into index fragmentation stats every day here :w00t:...