LBTC-

I do quite a bit of negotiating in my line of work

I think you need to ask for more information from them before you come back with a counter. At a minimum, you need to know for sure on a pension, health insurance costs and vacation. Add any extra cost to what you make now. I'd start with a number 5-10% above that, but let them know you have a little room to move. I would use numbers. I would also play this as you've going to be doing more/be more critical to the company than you currently are - therefore you need to be paid more.

Good luck!!

CA