We are observing the following phenomenon:
One of several SQL server 2005 (64-bit) instances is NOT using almost any memory. The database is not small (600GB) compared to the memory (64GB). This server underperforms compared to any other instance with the same DB. What's really surprising is that NO MATTER WHAT memory configuration we use, the server doesn't seem to ever use more than just under 300 MB of RAM. This seems like an obvious cause of slowness (let's face it, the SAN is good but not as good as cache, right).
We run the same process on dump-and-load copy of the DB on another server and it is happily chugging away (currently using about 24GB of memory) and the overall process runs 2-3 hours.
On the misbehaving server we're seeing 5-6 hours (about double!) and almost no RAM usage.