I have found similar issues.

Although I don't think they are remote hardware issues, here is why.

Remote. S70.
Vantage interface, asking status of 6 buttons.
In RS232 this is painfully slow.
Changing the commands to a IP command, the performance is much better, 2-3 times faster.

I think the issues is 2 fold.
1. That RS232 is just slow what asking lots of questions.
2. There is an inbuilt delay with RS232 devices, don't quote me on this but it is something like 400-600ms. I am not saying I understand quite how it works but it is there to allow sufficient time for responding devices to send all their data. Maybe this will improve in future builds.

Also.
It is worth noting.
The RS323 buffer is a first in last out buffer, not a fist in first out buffer like you may expect.

What does this mean?
If you send 3 commands, say 1,2,and 3.
NSP will buffer the commands and release them in the following order. 3,2 and 1.

D