My understanding is that Jruby is slower than regular ruby.   I take
this to mean the Ruby part is. (am I wrong in this assumption?)

Here is my question:   Currently 95% of the execution time of my
program is slow due to loading large quantities stock data, and then
processing it (moving averages, etc).   The actual  part I want to be
in ruby is fairly quick.

I expect to spend 20% of my PROGRAMMING time (in the future) working
with the "back end" (loading data and processing) and 80% figuring out
how to deal with the results. (hopefully ruby or another very high
level language)     The math (arrays) and the io is the slow part.

Would I get the advantage of the speed of Java I did the slow code in
Java or is it better to do it in C?      It looks like sharing data
between Java and Jruby is trivial compared to C.  Is this  fast or
does it take a while to translate?

I know the easy aswer is "do it in C" but I think it would be easier
to code in Java,

I have not actually tried this because I don't know Java, but it seems
like if I put a week into it it should not be too tough for what I
want to do. (load data, basic math, etc)

Basically I want help figuring out if I should spend weeks in C doing
the back end or if I would be satisfied with the (benchmark) results
of Java using Jruby and spend the time to learn Java. (which should be
simpler because it is much higher level)

Thanks in advance.  I hope I was asking the right questions.
Tom