As long as you go in with your eyes open it's a rewarding and well trodden path to take, and major MCs are usually very receptive to this kind of move. You will need to assume that your non MC experience will be effectively 'discounted' i.e. will be valued less than comparable tenure in another MC, so 3 years would give you credit for 1.5 - 2 years generally as a rough guide. That said you would be looking at circa late 30s to mid 40s for base salary. Key to making the move, aside of your technical expertise around lean will be to show how your internal consulting experience mirrors that of external consultancy - so bring across your stakeholder management, process design etc experience. Also internal cons making the move to MC tend to be taken aback by the culture a little, and this can vary from arrogance to 'quiet confidence'. If you can try to familiarise yourself with the target firm by talking to someone there before an interview and get a sense of how they present themselves.
