Matt,
As you have noted all Plasma screens creates IR (Infrared ) Interference to varying degrees, however more modern products have incorporated various techniques to minimise their effects which were not considered in the days when, say the BS3200 was designed.
Also, the Beo5 has an overall signal strength which is greater than the Beo4.
The IR carrier frequency used to control B&O products is 455 Khz, but the carrier frequency for your Pioneer is 38Khz and uses a different transmitting diode in the Beo5.
So, controlling your Pioneer screen with the Beo5 should be exactly the same as using the Pioneer's own remote control.
Controlling your BS3200 should be improved over the Beo4 mainly because of the increase signal strength.