There is a real difference in performance between PCI and PCIe 1x controllers?[/quote]Yes. PCI is maxed out at 133 MB/sec. This transfer rated is shared with other PCI devices.
There are some specific things I have to check before to buy about Linux compatibility?
If you are interested in running Linux on that computer you should of course check if this controller (or its chipset) is supported by your distribution.
Is it possible to use more than 1 controller or there is a high risk of conflicts, bottleneck or BSOD?
Works here. Promise PDC20579 and SiI 3512A on the same machine. No BSOD, but boot time is somewhat longer.
Any suggestions? Of course at a reasonable price
Want cheap? Then go for Silicon Image. You can flash most of them to non-Raid firmware.