I think space vs. looks is only a secondary thing to consider.
You will have to make a user study on this one. Especially if the form is going to be used a lot. With a good design, you could potentially save 15 minutes on every filling of the form and if the form is filled 1000 times a year, that counts for over 6 weeks of working time saved yearly. So, it easily justifies you going to the people and interviewing them for a couple of days. See what they think about it.
Some of the data is readily available. Some of the data may require some digging. Ie. going to another room, get some papers, come back to computer, fill the data in. Some, may even require the user to e-mail someone to ask for more information. And this information may take days to reach your user. Your solution should support that.
So, you come to a question where you have to ask yourself and your users which data is readily available and how should the not-so-available data be requested. What happens after that, when the user actually gets the information they requested and they're ready to return to completing the form.
You might be saying that oh, but they only start filling in the form when they got all the required information. But that's just promoting everyone to use their head, notebooks, sticky notes (which get lost, forgotten) or other means of trying to store information temporarily somewhere so they can some day start using the application they find not built for the task. This may become very daunting for the users since they need to revert using their brains for processing this temporary data. Even if they had a notebook or a sticky note somewhere, they need to use their heads to remember where.
So, in addition to sectioning the form, which I think @Rath_Er made a good example of, you will have to provide a temporary storage mechanism and an easy way to return to incomplete forms. Also, I would show a pill on the left side tabs showing a number representing how many of the required fields are missing. And when hovering the number, it would show a tooltip of the fields that are missing.