I personally believe as many ranchers pointed out that if you feel confident, you should go for it.
I think you are doing great on the mocks.
A typical suggestion is that, start scoring 85+% on the mocks, and you are ready for the actual exam with no worries.
If you have studied K&B book thoroughly, as I have read many success stories about the book, you should be fine.
But as it happened to me, I personally wanted to try a commertial simulator too.
So, if you feel for a commertial simulator, and if you want to try some, you should do it to be confident.
Per your request, here is the link for JQPLUS: http://www.enthuware.com/jqplus/
Here is the link for Whizlabs simulator that I tried: http://www.whizlabs.com/scjp/scjp-1.4-details.html