That would yield about 100 watts per cone. Enough to yield a noticeable difference.
Fair enough, I'll elaborate my opinion:
The PF210HE has two 16 ohm drivers (I just checked) run parallel, giving a 8 ohm load.
So, IMO, these are the options:
1) combine the PF410LF and the PF210HE as is:
Result: You can't dial up the mastervolume as far as with the PF410LF alone: no volume benefit
2) combine the PF410LF and the PF210HE (wired in series > 32 ohm):
Total speakerload: 6,4 ohm. This means the PF410LF gets 4/5 of the power, the PF210HE gets 1/5 of the power.
I don't think that's more than a 2db increase at best (don't know the exact formula I must admit).
But then the PF210HE is pretty useless as standalone cab.
3) Only use one driver of the PF210HE, a 16 ohm load and combine with the PF410LF:
Total speakerload: 5,3 ohm. 2/3 of the power going to four drivers (PF410LF) and 1/3 going to one driver (PF210HE, or better PF110HE).
This gives more or less the same situation as option 1) with the PF210HE again not optimal as standalone cab.
(and rewiring the PF210HE all the time...not my cup of tea)
4) Change the drivers in the PF210HE in one way or another, so there would be no power and/or impedance problem.
That would cost extra money and question is how the replacement drivers would sound (in combination with the PF410LF)
But that's just my humble opinion, maybe there's a mistake in my calculations.
Maybe some of the engineers could help out?