PHP on Linux box - Linux version for heavy site?

I'm sure this has been asked before but not since the latest and newest versions of Linux have been released. I'm having problems with yet another server provider whereas php4 sessions on their systems will not keep a session going when viewed in Netscape. The script has been tested on other systems off my providers and it works fine. So I'm thinking now I will setup a Linux box of my own, finish writing my site offline and then look at finding a reliable internet connection and connect my server box up there. My concern is I believe this site will generate a good 30,000 visitors a day which will be data intensive (GB of downloadable resources available). So I'm curious is there is a particular version of Linux I should consider that's better for higher traffic sites? Or am I dreaming to see a free OS product keep up to purchased OS such as SunSolaris? I've found lots of opinions but I haven't yet seen any real comparisons. Any useful information or real personal experiences (not stories only heard) would be greatly appreciated. Or if you know of a good provider that offers PHP4b3 or newer, MySQL, offers reasonable prices and has a good track record then I can bypass the extra learning curve (or expense to hire someone) of setting up a Linux box. Thanks, Jason Carlson