Kawa versus SISC

[Chris Bitmead]

Hi,

I'm trying to get some version of Scheme to be the programming language 
in a government project I'm on. I was just looking at the comparison 
below...

http://sisc.sourceforge.net/comp.html

On the one hand I'm impressed by sisc that it fully implements r5rs, 
including full continuations. On the other hand I like that kawa seems 
to be mostly faster. Even better that it can be compiled to C for even 
more performance.

There has been brief mention of kawa supporting continuations in the 
future. Would doing that do so much damage to the java memory model that 
kawa's performance degrades to the same point as SISC? (like 
full-tail-calls currently cuts performance in half (?)).  

How much work would be involved to upgrade Kawa to full r5rs?