Other than 2 range do they increase the packet speed more than usual?
Not according to the documentation. However, the wiki doesn't mention that Collectors become 140% as efficient on a PZ, which has come up before, so you may be right...
You could test it in the map editor.
Okay so I decided to do some testing myself.
I made to relay links about 220 block long.
Relay 2 had power zone.
Relay 1 didn't have power zone.
What I did is I deactivate both of the first 2 relays. I had a shield in the middle and end on the relay. I then pause the game and activated both relays at once.
I then did the same test with packet speed 5 and 39.
At packet speed 0. I found there was no difference.
At packet speed 5. I found a very slim difference, barley noticeable. Relay 2 being ever so tiny bit faster,
At packet speed 39. There was about a 0.2 second delay between the relay 2 and relay 1 with relay 2 being faster.
Basically, the power zones do make a difference however the difference is so small. Its almost as if it isn't even there. Once you get packet speed high enough to notice a difference. The packets would already be going from 1 end of the map to the other in a couple of seconds.
Note that no matter how quickly packets are traveling, they will always stop for one frame on each network element they use. Hence with absurdly massive packet speeds, the increased connection range is itself a slight speed advantage. (This also applies, to a slightly lesser extent, to CW1, btw.)
It's possible the node delay is the entirety of the speed differential being observed. You'd have to also test with relays on power zones, but with normal relay spacing, to verify. I don't think it's enough of a difference to affect play, though.