Which hardware to buy for Informix-Online? (AIX,HP,SUN...)

My company is running I-Online on an AIX-RS6000-320 machine which is getting to be to small. So if we are going to buy a bigger machine, what is the best buy when considering Informix management (admin., backups, raw partition management, hardware maintenance a.s.f.). We are talking about less than 100 users and probably less than 40 heavy duty users, and data that fits wery well on a 1gb disc. And while on the subject, what do you folks think about having a seperate test machine for testing, and how like the running env. does it have to be? With thanks in advance, Gaukur. gaukur@rhi.hi.is