Seeking insight from heavy lifters

A manager friend of mine sent me the following concern. He's preparing to
shift to Postgresql from a proprietary DB and 4gl system:

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To that end, I've also started studying up on Postgresql. It seems to have
all the necessary features for a transaction heavy DB. The recent release
is 7.3. Of course, "the proof will be in the pudding." We average 2.5
million transactions per day or 800 per second. Unfortunately, we would
have no way of testing that until we committed to getting the business logic
moved over and had something to test it with. This is a bit of a "catch 22"
situation. Just wished I knew of someone locally who was running Postgresql
in such a heavy environment. I'd love to find out how it performs for them.
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While I have a lot of experience with PG, it's not really been in a heavy
processing environment. Could I get some input to send him from anyone
out in the field using Postgres in a similar environment.

If PG isn't the best option here, what is?

Thanks very much for your input!

John