Good Catch-All HMC version

Hi All,

I just got my first Power7 machine and when hooking it up to my HMC i found
the "version mismatch" error. That particular HMC is at v7.7.3 and the fw
on the p7(al740_110) requires v7.7.4
Taking into account that my lab has machines ranging from the venerable 150
(which i'm re-installing to attempt data rescue of a client's tapes) to
this shiny new/used (ibm remarketing) 720 (8202-E4C) i was wondering which
version of HMC code is recommended to support this wide range of machines
(I mean, of course, Power5 to Power7+, not the 150).
I also got a new HMC so i have one CR3 and one CR4 so i could have two
versions running (i know the recommended level for P5 is v7.3..5 but my
v7.7.3 worked without problem with them).
To make it short. Do i install v7.7.4 or do i go all the way to v7.7.8? In
the readme i saw some info about partition info taking more space on .8
which meant that some systems wouldn't be able to upgrade And that managed
systems managed by that version can't be later managed by older versions (i
believe that it only means that partition info isn't backwards compatible,
a full reset of the FSP should make it work again with any supported HMC
level, right?)

Thanks a lot!

PS: What does ECA 331 entail? searching for data on supported HMC levels
for that i found the advice regarding fw update on p7 and that ECA...