Slow and steady wins the race.
Cliché's out the way (although I do think it's true), one of the things I find with writing is that you should always stick to what you're comfortable with, unless you're finding it detrimental to your writing.
So, if you're doing 250 words/hour, and feel that's too slow, then I would suggest you set yourself an easy target. Double it to 500wph, or increase it to 1000wph, and try achieve that.
If you can sustain it, and feel that it's easy, then up the ante again. If you find yourself struggling, then lower it.
The best thing really is to experiment, and find the level that you feel most comfortable with.
Edit: I also wanted to add that, according to this article, author Dean Wesley Smith says:
“Most professional writers can average about one thousand words an hour, when going on a novel. Not in the struggle of the beginnings, but once the novel is underway. So, simple math says that to write a 90,000 word novel, you have about 90 hours of work.”
That would suggest that you should set your own expectations based on where you are in the process of writing your novel, but I still recommend sticking with what you feel comfortable with. With practise, your wph will likely start to increase naturally by itself.
The word count for a page will vary depending on font size and type, margin size, and spacing elements (single/double space, blank lines, subheadings, graphics).
For a page with 1 inch margins, 12 point Times New Roman font, and minimal spacing elements, a good rule of thumb is 500 words for a single spaced page and 250 words for a double spaced page. Using this as an example, a 3-4 page double spaced paper is 750-1000 words, and a 7 page double spaced paper would be 1750 words.
Assignments often specify a research paper or essay length in terms of words, rather than pages - a paper of 750-1000 words or a paper of 1500-1750 words. This way a student's paper will still meet their instructor's length expectations, regardless of varying font size, margin size, or use spacing elements.
When viewing an electronic version of a student paper in MicroSoft Word, the exact word count can be easily determined. Some research assignments require students to include the word count of their paper.
Also, clarify with your instructor whether the words on the title page, abstract (if used), and reference list count toward the expected word/page count.