Went ahead and tried it. I was able to replace the CX-2G-146 drives with CX-4G-73 drives by replacing one drive at a time and waiting about 1 hour between drives. After the upgrade was done, I was able to reset the back-end bus speed to 4Gb. Worked fine.
We have a CX3-20 array with a single DAE4P and 5x vault drives (CX-2G10-146). The array has no Raid Groups/Luns/Hosts, and is basicaly blank/empty. Our goal is to replace these 2Gb drives with faster 4Gb drives and boost the bus speed to 4Gb.  Im thinking that I could replace the drives, one at a time and allow the array to update the FLARE/OS replicas onto the new drives. After all the drives have been replaced, I should be able to perform a BUS speed reset which would boost the loop to 4Gb.  So, is there any reason this could fail? Questions: 1) Is this possible to do using the method I described, or perhaps a different method? 2) How does one tell if/when the FLARE/OS code has been deposited onto the "replacement" vault drive?  Please let me know if this looks like it should work. Thanks
User upgrade for vault drives?