I would say if you try to get more than 40K, you'll be pricing yourself out of the market. The 58 is one of my favorite pistons to fly, but there are a lot of people out there with about the same experience as you that will do it for next to nothing (which makes some owners skeptical of their ability) just to build the time. Remember, that if you do score medical, dental, etc., that stuff costs them much more than you think and would put you at a cost to them of over 50K+, even though you'll get 40K, etc. Don't forget to work out a per diem so you can eat.....or maybe see if you can get "actual expenses" reimbursed.
Maybe I'm totally wrong, but if you go too high early, it'll be tough to ask for more down the road.