The faster processor will save time in render times… so in 3 years of it… it pays possibly.
Buy the RAM from Apple this time… it’s not much more than Crucials… And you only deal with one company for warranty that way.
The SATA question is a lot more “touchy”… internal SATA’s not part of an array will do 8 bit uncompressed and lower only… HDV? yes. DVCPROHD, yes… uncompressed 10 bit or uncompressed HD? NOPE… you need an array for that. Stripping 3 of them internally may not give you enough speed for uncompressed 10 bit HD.
You only need one card to run BOTH of those monitors. I’d buy the Radeon, because Motion, Photoshop, Arpeture will all benefit from it, and running Two displays cuts the VRAM in half using one card…
Jerry