Help, need information comparing Informix to Sybase and Oracle

My company manufactures computer hard disk media. We are planning to change databases and I would appreciate any information from people that have experience with Informix and either Sybase or Oracle. Our application is a realtime data collection and analysis system for automated test equipment. The Operation runs 7 * 24 hr, no down time. The data rates are relatively high. We are currently using Raima's db_Vista, which fast but lacks tools and has very little protection. Data rates 2 to 300 k bytes every 1 min from each of 150 testers on an ethernet. About 10 users accessing data and 10 pc's running to parse incomming data and update the dbms. We are now using Netware and are considering to switch over to a Unix box, HP or SUN for reliability and programming tools. I would like to have better 4th generation tools avialable that can do textual reports and realtime graphics reports. 1> Which makes more sense Unix or Netware? 2> If Unix who makes best hardware, provides best documentation and support? 3> Which database makes the most sense, reliablity, efficiency, speed, tools, administration? 4> Which allow for the greates use of third party tools. 5> We need a gateway to the AS400 that would allow joins across the net, which provides the best solution? 6> We will still have netware servers and would like to use IPX, SPX. Any problems? 7> We use c and C++. Compare the products, embeded sql and a CLI. 8> Tuning, how easy and how neccessary? 9> Are there utilities that must be periodicall run that require downing of the database engine? 10> Which database is the easiest to use? 11> Support? 12> What other questions should be asked?