Go with the ST40
I just bought the ST40 BiData with Transducers. It cost me $265 off Ebay from a Raymarine dealer and it included the 2 transducers. I knock out the old ones installed the new ones and hooked it up. I will probably buy the ST60 displays off Ebay used and have a nice pedistal mounted setup as I will be putting on the 4000 Autohelm, and want the head units to look the same. I will use the ST40 as a "backup unit" although technically it would be the primary as the transducers plug in to it.I also bought a great SeaTalk to NMEA converter which I modified to be USB and have it running with SeaClear on my PC which gives me full moving map display with depth, waterspeed, log etc.All works so far!!!