Mixed RPG/Java performance (was: EJB versus RPG/COBOL)

> So overall what I think I'm hearing is...
> that aside from personal preferences as a developer,
> and the cross-platform issue, developing a server-side
> app (to run on a single as400 server) using mainly
> Servlets/JSP's for the web interface and coding most
> of my Business Logic in RPG will not only work well,
> but it will in fact produce the faster performing
> application (which is the real key here)... correct?

Against my better judgement, I'm kicking my thoughts into this debate.

First, I think there is a distinct need to define what sort of mix wer're
talking about.  We can have an RPG program directly invoking Java classes.
We can have a Java servlet front end that calls existing RPG programs via
PCML/toolkit and directly returns data as parameters.  We can have a servlet
use JDBC that calls a stored proc which in turn wrappers some existing RPG
programs.  We can have the servlet do JDBC directly to the database and have
RPG trigger programs to validate RI.

In any and all of these mixes, we need to be concerned about validation.  Do
we call RPG (the business rules) to validate every field on a form?  Write
Java/Javascript to pre-validate?  How much duplication of validation do we
use in for the sake of runtime performance?

I have heard over and over how fast a mix of Java and RPG can be, but my
experience in trying to reuse existing RPG programs via parameterised
toolbox calls does not support that.  I can get about 3 calls per second on
a big 820.  I can validate the input with one call, but what goes on the
panel depends a lot on the underlying data.  I have a 'show me my telephone
bill online' application in mind.  I extract the stuff that shows on the top
of the bill (the summary) with one program call, I run out of parameters
when I want to show the monthly charges (phone line, taxes, etc.)  So
there's another program call for the monthly charges.  Then I have to show
the long distance, carrier by carrier.  Because only 64kb is available to be
returned via a parameter list, that requires a stored procedure.

You start to get the idea.  By the time I am done with my particular mixed
Java/RPG application, it has taken between 8 and 15 seconds to display one
of the various panels in the application.  This is not what I would call
blazing speed.

Can somebody explain just how I am supposed to reuse my existing RPG
investment with decent performance?  Or is 10 second average response time
going to be declared 'good enough?'
  --buck