Its amazing how much they charge for memory. I have a HP 1100 with the default memory (1 MB I think) and I have had problems in the past tyring to print high resolution images. It would only print part of the image. I think laser printers use memory differently than ink jets. I think the entire page has to be loaded into memory before it can print. If you can't fit the entire page into memory then it only prints part of the page. Laser printers print the page in one sweep, unlike ink jets that print line by line. Someone can comment if I am wrong.
More memory may not speed up your printing, but it will allow you to print more complex images. I think the speed is largely based on your computer and printer processors.