Multiple H1B's and multiple employers at the same time


Registered Users (C)
I am currently on a H1B visa working for a company X that holds my H1B (no third parties, directly with the client--Perm job with the client). I have an offer from a different employer Y that is sponsoring a new H1B for me (in this case I will actually work for the client of this employer). I have 2-3 weeks of vacation that I accumulated with my current employer X that I would like to utilize and not waste before moving to the new job. Also since the offer that I have right now is actually to work for a client of the employer Y and be paid by the employer Y (as a consultant), I would like to see If I can take a paid vacation with my current employer and then go and work for my new employer Y and then depending on how it goes up there, either return to my current employer (If I dont like the new job or for any other reason) or actually at the end of my vacation period tell my current employer X that I am not coming back and resigning to my job. In this case, Is it ok to be paid for the vacation period with my current employer X as well as get paid for the work that I do with my new employer. What are the limitations and any legal or immigration implications If I do this. Is this ok to do at all? Please let me know. In this case I will have twe H1B's at the same time untill one of them actually cancels it after I inform my resignation.