600 is not bad at all...
You will want jack to Node 2i to also be at least 5e otherwise it would not be getting the full Gigabit. Is yours 5e?
If you replaced the jack to Node 2i with Cat 6 your not going to see any improvement, you would still get the same 5e speed. Again if you are considering going to a high quality cable like Wire World for improvement someone else can address that.
You will want jack to Node 2i to also be at least 5e otherwise it would not be getting the full Gigabit. Is yours 5e?
If you replaced the jack to Node 2i with Cat 6 your not going to see any improvement, you would still get the same 5e speed. Again if you are considering going to a high quality cable like Wire World for improvement someone else can address that.