Processing Time & Risks with H1 Amendment & H1 Extension at the same time?

Hi, I have my first H1 from Oct 2013 - Sep 2014 (No stamping). I got my H1 approved from Client A in April 2013 but from September 2013 I moved to a different state and now with Client B. I want to go to India in May 2014 so I my employer will be filing an H1 Amendment and H1 extension (in April) the same time in Premium processing. My questions/ concerns are:

  1. Client B can provide a client letter only till Dec 2014. They say its yearly basis. I can make them add a word “possible extensions”. But concern is since I already have valid visa till sep 2014. Is there a possibility of uscis denying the extension because according to dec dates; I need only 3 extra months based on the letter? Is the probability of approval higher if I renew in june/jully instead with same client letter (dec 2014)? I really would like to get it stamped till Sep 2015 minimum if not till 2016.

2.Since I need to go to India in May, I am planning to get premium processing. What is the processing time for “Amendment” and “Extension” in premium processing. Is it 3-4 weeks for Amendment and then 3-4 weeks of Extension. Or both happen at the same time and i get the results in 3-4 weeks once applied.

  1. Does Applying for Amendment and extension in the month of April delay the process or increase the risk because of the new year H1 visa filing month ?

  2. Any other pre-requisites that are required before filing an Amendment and extension? I am trying to find out if I can fly out on May 9th/ 16th or later?

Please let me know. Thanks so much in advance.