I would make them make you an offer, then you can see what they think your job role is worth. Then negotiate from there... if negotiation is required
If you say your currently on X + 28%, then they could reduce their original offer to suit, or I want X + 45%, they may ay thanks but no thanks
At the end of the day, yes money goes along way, but for me job satisfaction tops the list. I could think of nothing worse that despising the job I was doing. Would I take slightly less money for a more enjoyable, prosperous role... Yes.
Also a word of caution, I have been caught in the "prospective employer promises" trap before, so don't take everything they say as given. I was promised shares once...... have they ever materialised..... errr No
Good Luck