The 'problem' is if you're running the RAM at DDR3-1600 on any AMD Phenom (x4 or x6) without either a FSB -> 240MHz <or> CPU-NB Frequency -> 2400MHz then it'll be unstable. In addition, quite often the 4GB densities require a BIOS update.
Q - What EXACT set of RAM ; please provide a link.
Q - What BIOS version?
Next, the ASUS M4A87TD EVO won't/doesn't support SLI. However, most of the new AM3+ 990FX do support SLI; you just need to double-check.
Q - What budget for a new AM3+ MOBO?