[TenTec] Paragon Firmware vintages and compatability

[d.e.warnick at comcast.net]

I'm trying to figure out which levels of TenTec firmware are compatable with which vintages of hardware. I found nothing in the archives, so here is the long question:

I have 4 Paragons

Ser No          Chip Mfr          Firmware Version          Hardware
585-00681    TenTec                 3.4                             Old???

10B10409     TenTec                 3.9                             Old???

70A10172     Giehl                     6.1                             New???

81A10289     Giehl                     3.0                             Old???

Spare Chip     TenTec                 4.0                             New???
This spare chip was included with one of the Paragon's that has a Giehl chip installed

OK, here are my the questions. 

I plan to upgrade 10B10409 with an N4PY chip.
Can I install the 3.9 chip in 585-00681 to upgrade the 3.4 chip?
Would the 4.0 chip work or is it for new vintage hardware only?
Is there anywhere that I can look at what the various vintages of TenTec firmware did?
Is there any point in considering moving from 3.4 to 3.9 on the older rig?

Thanks in advance to anyone who can provide part or all of the answer, or who can point me in the right direction to find it myself

Dave
WA3MKB