Do everything you can to not burn bridges, but that seems highly unlikely. If you are the most skilled though, they can't refuse to want you back though. If you are just a normal run of the mill guy, don't expect it. Is there anyway to talk to them about being offered a job, without leading on that it is the client? As in, say you have found a job opportunity out there that is offering you a,b,c, and would like to give as much transparency as possible. Giving them the chance to match your need.
Or the best choice may be to simply go to them and layout what you need in order to be happy at your currnet job. Explain to them that you've been there so long, worked on high level this and that, and lay out your case as to why you deserve everything you are asking for. I strongly urge putting the same thought into the as you do your work. Turn your investigation inward and datamine your career for every piece of information then write it up in an organized way that makes sense much like you would any other code. Then after you've laid it all out, if they say no, you can say thank you, but this is what I need so I will let you know that I'm going to start looking elsewhere. This gives you an out to say, I gave you the opportunity, you said no so I told you I would look elsewhere. Logical place would be your current client, and you'd be doing the looking not them. This also gives you a buffer that isn't a abrupt two week notice. They may not think you are going to actually start looking immediately, or even have anything in mind. So this could give you a little more time to work out the deal with the current client.
Now, that aside, the actual decision here is probably the most gut wrenching. I went through the same type of thing a few years ago. I moved to Chicago for a job. One of my best friends got me hired with him at a (now) 3 man shop. It was an excellent job, good benefits, great boss (most of the time haha) who I looked at almost as a mentor. I worked with my best friend. It wasn't too demanding. Got to travel some, very interesting and stimulating at times, couldn't be happier. Except, even though we grew to 5-6 people I still seemed like the 3rd wheel underling, and got paid accordingly. Even when I helped hire people into two positions over me, (and my friend) and while we were really the show, I never really felt my title. But it was stable, I could probably have worked there the rest of my life. But an opportunity came along that was about 15k more a year, and all sorts of other things. It sounded great and was going to be great. It scared the shit out of me. I didn't really know these people, the knowledge was a bit over my head, it was working out of my home, with lot's of travel which I don't mind. Still a small company, but different entirely. But in the end I decided it was what's best for me. I was getting married, the money would help, the experience would be great and the people can't be too bad.
It was a disaster. The company was small with 3 bosses and none of them took charge. Everything got defered to the others, and nothing got decided on without pulling teeth. My role was never clearly defined. Professional Boundaries were crossed all over, the people were the best at what they did and were great people, but it was just a clusterfuck of a business. I couldn't sleep, I practically got an ulcer, and eventually we all came to an understanding that it wasn't the best situation for me. In the end though, I'm glad I did it. I was unemployed for a couple of months but was lucky enough to use my connections to get a new job. And the best part is, I stayed in the price range and level that I had worked my way upto. I didn't drop back down because of the failed experiment I just plowed through to the next thing. I still probably love my first job best, but i've found an inbetween of stable solid work and money. I have never regretted it. Sometimes the best experience is the experienced gained from taking the chances if you believe in yourself enough to land on your feet if you fall.
**** that sounded like a motivational poster with a cat on it.
