I am not a professional coder by any means, but merwais is correct.
PHP script could only handle 11,000 peers then the server would be at 30+ (over 5 is bad).
Then my coder, who did do it for a living, got sick of the code, made his own, first thing i said was, can it get more than 11,000 peers, he was yeah np, put it on, guess what, got to 11,000 peers, and boom lol he was scratchig his head so much he just gave up and i havnt spoke to him since lol that was nearly 3 years ago.
even gazelle comes with XBTT, they have been saying for awhile that they are working on a PHP announce, but so far, as far as i know it has not materialized yet.
Maybe with a lot of servers, and memcache and other apps that they have for servers, it could push out a lot more, but on 1 server with no fancy gimmicks, it struggles big time.
even XBTT struggles with more than 100,000 peers if you have announce logs on, but if you dont have them on, it "should" be able to get up to 400,000 pretty easy.
Only way you will ever get 5mil peers is with a hell of a lot of servers, all beefed up to the max with hardware and software, no ratio, and dare i say it, only log announces every day, not every 30 minutes like most sites do.
11,000 peers to the announce every 30 minutes 24 hours a day 7 days a week = 6 queries a second to the db, may not sound like much, but that is only from the announce, nothing else.
as far as i know, no one knows what to do about it, there is a new streamlined PHP announce out now, but as we have used XBTT for 2 years, i have no idea how well/bad that does, but atm i am pretty sure, that if you want a fare few peers, you will need XBTT.