Perception of progress – amount of pages

I'm at the very beginning of redesigning a checkout/bag page and had a thought about how people perceive their progress through a form based on the amount/lack of pages.

Currently we have a bag page which clicks through to the checkout, the checkout is a single page.

My plan is to merge the two into a single page and integrate the sign in process for users without an account (you need an account to complete the purchase).

Would users feel they are making more progress towards their goal if they navigate from page 1 to page 2 or would the fact they only have to complete actions on a single page to achieve the same goal make it seem quicker for them?

So in short, do I go for two short pages or one long one?

(Page load of the long page isn't an issue, the difference is inperceivable)