The only difference in
Traffic Proritisation between Pro and Option 3 is the latter classes P2P, Usenet and Other as Silver not Gold. Gaming is classed as Titanium on both packages.
This means that Titanium classed protocols are given priority over lower Gold, Silver and Bronze classes.
At peak times, packets classed as anything below Titanium are dropped by the network which induces artificial packet loss, preserving bandwidth for Titanium packets.
This is happening by design, although the intentional design is to have no Gold packets dropped during peak, after a couple of years of Ellacoya tweaking, Plusnet have not yet managed to stop Gold packets dropping.
Therefore, even though protocols on Pro are not throttled, they are subject to induced packet loss during peak times.