PHP5 hosting is not a niche... any respectible (and lots of not so respectible) host(s) should be offering PHP5 - not least because PHP4 was EOL'd at the start of the year, and the PHP Group officially stopped providing security updates for it in August (
http://developers.slashdot.org/devel.../2349228.shtml).
EDIT: You may also find this interesting -
http://www.nexen.net/chiffres_cles/p..._july_2008.php
I'd also like to clarify that, contrary to your post, Google has not "recommended" any particular hosting provider - but I suppose what you mean is that they turned up in a search result for "fastest possible PHP5 hosting" or something like that?
Unfortunately, although there are many ways that you could potentially compare different hosting providers to attempt to learn which might be "the fastest" it will be a pretty pointless and fruitless exercise - each test would give you a different answer
Instead, I think we need more details about exactly what you're looking for, what you hope to use the hosting for (i.e. what's the details of the site/s and where will the visitors be?) and finally - what's your budget?
The fastest host is undoubtedly you if you buy a big fat dedicated server and colocate it in a nice well connected place... but I'm guessing that's a long way past your budget for this project?