Generally it is not recommended to update iDRAC firmware to very old version to latest. I will recommend to update to 4.00.00.00 first then to 5.00.00.00. 
I got some R640 servers and the current iDRAC version on them varied from 3.21.21.21 to 3.36.36.36, and would like to upgrade these servers' iDRAC to latest version 5.00. however,  I'm not sure whether I should "upgrade them to a later version then to 5.00" or it is just fine to "upgrade them directly to version 5.00"??? Note that the iDRAC 5.00.00.00 did not describe such limitation, as shown on [URL] but I still wonder... if i upgrade iDRAC from a version that is too old(e.g. 3.21.21.21)...would that be okay actually?
R640 upgrade iDRAC prerequisites for some specific version???