Database decision

Hi, I do not want to start a big arguing here but still i am kinda curios what you say is the most powerfull DB-Engine to run on a Linux-Intel based PHP4 System. The project I have is an article based system. Many relational cross-references for using articles in different online projects. Well, I need a decision now for what I system I should use. I guess a cannot afford the 5000$ for an Orcale, but if you say that this would be the one and only choice ... Currently I use MySQL for doing things like that, but I think I have reached a point where MySQL will come to it's limits. Or what would you say would be the maximum a MySQL-Based thing can handle? Maybe it not MySQL is coming to it's limits but, rather my programming skills are??? Anyone one of you know a place to look for advanced php programmers who would be interested in working on a job like that? Thank you very much, in advance Alex