V8 has a very impressive garbage collector (stop-the-world, generational, accurate) and the GC is probably a part the Google team have spent a lot of time tuning and working on as it's one of the harder and most important parts of building a VM...

My guess is that node's GC configuration isn't finely tuned for 25KB structures or maybe the GC is called prematurely.

Some suggestions: try to turn off the GC and re-do the benchmark, try with smaller JSON datastructures, try with different versions of node. Each of these would give more evidence where the problem is.

Btw. in that benchmark: which versions of RingoJS and node.js are used? How much memory does each server use in the end?

Edit: What type of garbage collector does RingoJS/Rhino use - how is the GC configured for RingoJS?