Options to improve performance accessing Outlook folder data

I have an app which runs fine and performs as it should, except that it is very slow when accessing other users Outlook calendars (located on remote Exchange servers).

My app is written in C# (.Net 3.5SP1) and I am using Outlook Automation to read the data.

I know that some other options are:
CDO (not supported in .Net)
WebDAV (requires something on the server, which I have zero access to)
Redemption (I have no idea if this is supported in .Net)

Having poured over countless articles and tips on the web about maximizing performance of Outlook automation, and lots and lots of testing, I am pretty confident that my existing code is as optimized as it's going to be.

Any other suggestions? I an read the data synchronously (one calendar at a time) or asynchronously using mulitple threads. Doesn't seem to make much difference.

One thing I have observed is that if I read some calendar data, the next read (if withing a short time period) is much faster... as if the first read "seeds" a cache somewhere in Exchange with the data, speeding up subsequent reads.

Bottom line is the performance is intolerable when trying to read more than 3-4 users calendars.

Any help is appreciated.


** Update ** - I experimented with WebDAV, but quickly learned that it does not support recurring appointments. That is a deal-killer. Also researched Redemption but found that it is (from what I read) not any better than OOM.


I do not know where to turn to next... I guess