Well, you've already gone right past the limits of my concrete knowledge--I thought you were asking a very different question (about DEVELOPING an Access project as a team via the web).
However, based on what you've said above, it sounds like Access + WAN = bottleneck, so I ask:
Is it possible to either...
(1) use a web-form front-end instead, or
(2) install the FE locally to send and receive JUST the SQL to the BE, so that the data isn't replicated locally at all?
Bear in mind, these are just blue-sky suggestions. You need to get Pat, Jack, or one of the other list gods to help you with this one.
--Useless Mac