H-1 B Extension advice on portability

[pkb16]

H-1 B Portability Issues. I’m working with employer ‘A’ and my current petition with employer ‘A’ is yet to be approved. I got RFE and responded back on Aril 3 2015 and still waiting for the update from USICS. And Now I got an offer from employer B. B is ready to file the petition for the transfer of my H1B visa as soon as I get approval on my current petition with employer ‘A’.
 

Now my question is:

1. Will there be a problem if employer B files for H-1 B transfer before the transfer petition filed by employer A is approved?

2. As employer ‘B’ has been waiting a while to get my current petition approved. They gave me two options as I have a current and valid H-1B visa stamp in my passport until February 2017.  I have the ability to leave the U.S. without needing to obtain a new H-1B visa stamp in your passport. 
 
 First option- Employer ‘B’ can file H-1B petition with a request for port of entry notification.  Under premium processing and have the approval in place so that as soon as my current H-1B extension was approved. I could then quickly depart the U.S. and come back into the U.S. with current and valid H-1B visa stamp in my passport and the employer ‘B’ H-1B approval notice.
 
Second option - we will just plan to move forward with the H-1B change of employer as quickly as the current petition is approved.  Which option to go for based on my situation? Employer ‘B’ has been waiting for a month now.
 
3. If I go with the first option and I get approval. Will it matter, If my current petition gets approved or not with employer ‘A’? If it is not will I be out of status? If leave country and come back on employer ‘B approval petition, Will I be back on valid status?

Your help and advice would be greatly appreciated. 

Thanks!