I can't speak to what the newest version of the 13" rMBP is capable of, but I can offer that my late-2013 15" rMBP and a 2014 15" rMBP (both with the discrete GPU) cannot drive two 4k monitors at 60 Hz - the can drive one 4k monitor at 60Hz over DP and one at 30Hz over HDMI. I have two Dell P2715Q (Rev A) monitors on my desk, both connected to my rMBP. I can daisychain two 4k monitors and mirror a desktop @60Hz but can't extend a desktop at all - a limitation of the OS and/or lack of proper drivers IMO.
There's a very long thread in the Mac Peripherals forums about the two Dell P-line 4k monitors that will offer the same sentiment as I'm offering.
There's one member, larrysing1963, who's driving one 29" (I think that's the size) LG Thunderbolt monitor and one P2715Q monitor with a 15" rMBP with an integrated GPU (I think they're daisychained, but you'd need to confirm that) - I'd suggest consulting with him.
As to the Samsung monitor, that's the old 4k tech. We tried two, they were IMO junk and went back.
I have hope that 10.9.3 will offer better 4k support. I've also installed nVidia's CUDA drivers, to no avail. I can connect my two P2715Q monitors to a Windows box here in the office and drive both at 4k either daisychained or via the two DP ports in the (really cheap) AMD video card.
My next purchase will be a riMac, and I'll connect one of my 4k monitors to that unit.