native code performance

Hi,
I've been experimenting with using gcj native binary compilation for the 
following problem.
I'm seeking to integrate the weka machine learning toolkit in a C++ 
program. Weka is 100% java code.
I've learned about CNI and it sounds quite an appealing solution for the 
integration part. However, before writing the C++ code, I tried to see 
what the performance are when the java code is compiled to a native binary.
Basically what I did was the following:
I compiled the weka source code using gcj (ecj) to a .jar (bytecode).
I wrote a simple program that actually uses the toolkit to run a classifier.
I compiled this program into a class.
I linked everything into a native binary with the -findirect-dispatch 
option.

As I'm new to gcj I might have done something wrong during this process, 
but it seems alright given my understanding of the gcj manual.
Although I actually don't know where I should have enabled the 
optimizations (-O2)

Now comes the unattended result.
I ran the native binary and it took 13.4s to execute a classification test.
When using sun's java, the program (in this case the .class) executes in 
3.2s!
I had expected a native binary to outperform the VM.

So here my question is very simple: is this result realistic or i'm just 
missing the magic to speed the native binary up?

Thanks


-- 
Marco Canini