Re: Would it help to use munchkin code instead of the form itself on the landing page to help load time on form submission?
Any data that must make it to your Marketo instance needs to travel the globe to that particular server.
For example, if your Mkto target is in San Jose, even though the scripts that initialize both Munchkin and Forms 2.0 can be loaded from servers close to China (via CDN) -- which is great -- the user-supplied data can't go just to the CDN but must go all the way to San Jose.
Munchkin and Forms 2.0 are both bound by this same technical constraint (which isn't unique to Marketo!). There is a way to speed up the apparent speed of the post by performing it as a background task (it still takes the same amount of time, but the user won't experience a delay). Note if you use this method you may end up sending people to a Thank You URL before the post is actually complete (i.e. it's still sending data but you're saying thank you). Not that this is a big semantic problem, really, but you should be aware of it.
You will need a skilled client-side developer to implement the background post.