I just moved to a new company so I can talk about the H1b transfers. When you apply for a H1b transfer, currently it is taking 8-9 months before you can get the final approval. You can however work for the new company while this process is going on.
That said, you (or your employer) can pay about $1k which sort of puts your application at the top of the pile. If you go down this route, you end up getting the approval in about 2 weeks.
There are reasons why people choose premium processing. For example if they have to go out of the country within the next 6-8 months, it is best if you have the H1b approval documents with you.