Concur, 890GX chipset better choice. Note the native chipset driver for either one does not support Trim, Must use the default microsoft AHCI driver (msachi). Also trim is only supported in Win7, not vista, nor XP.
To the best of my knowledge the only drivers that will pass trim are the uSoft win7 driver and Intel's latest AHCI driver (ver 9.x).
Based on a previous post (believe by randomizer), the C300 (internally uses the Marvel controller) can booge down with out trim cmd. Its " garbage collector" is not as good as that found on the SATA II SF-1200 controller SSDs.
GF6150SE is very old! It surely does not have SATA 6Gbps, or are you using an add-on controller in PCI-express slot?
The SB850 southbridge supports 6 x 6Gbps SATA ports, so yes this is what you want. However: DO NOT USE the AMD I/O driver; this will cause you to lose TRIM! Run in AHCI mode and use Microsoft AHCI driver. Check with AS SSD which driver you are using (should say msahci).