Domain registration: Multiple keyword domains vs. one domain in same Niche

Basically what I'm asking is whether you guys think the benefit of having multiple exact/phrase match domains outweighs the benefit of having all your backlinks link to the same domain?

Here's a hypothetical. You have 5 longtail keywords in the same niche you want to target. You're selling the same product, though you have tweaked the landing pages for each respective keyword. Which approach would be better from a purely SEO standpoint, ignoring for the moment the intangible branding potential that having all the sites under one domain may provide:

Have 1 domain name that contains a couple of your keywords, with 5 pages that have file names like keyword-goes-here.php, and a hundred backlinks to each page.

Or,

Have 5 domain names that are very close matches/exact matches to their respective keywords, with a hundred links each? Assuming we also link the 5 pages to each other.

I'm relatively new to SEO, so it would also be extremely helpful if you could elaborate on the factors that go in to your decision.

One more questions is whether you think you're better off with a .com/net/org that is a phrase match (e.g. mykeyword.com), or a .info/local domain name that is an exact match (e.g. mykeyword.info or mykeyword.ca)?

Thanks in advance for your all your help.