Well I don't know for FTTPod, but FTTP (300/30) Infinity 4, when we had speed issues (i.e. our 300Mbits dropped down to 45Mbits) BT told me on the phone before it becomes an issue (i.e. listed as a fault) when it drops below 40Mbits (downstream) and that the minimal guaranteed downstream speed was around 40Mbits which I think is stupid for the 300Mbits package, as for the up there was no guaranteed speed.
I can see with the new 300/50 that the guaranteed speed has increased to 100Mbits, but good luck in getting that form BT, BTW DSL Checker says I can get 330/50 yet BT says I cannot.
What you need to also take into account is that the fibre going into the splitter can handle about (2.5Gbits down / 1.2Gbits up) now that fibre is split 32 ways meaning if everyone on that split fibre had Infinity 4 (300/30) and everyone hammers their connections up and down, your speed to the Exchange would be 78.125Mbit down and 37.5Mbit up.
So the amount of users and what package along with how many connections the ISP cram together would both affect what speeds you get hence the 40Mbit guaranteed speed.
I assume that BT will upgrade their infrastructure with the 300/50 due to like I said the minimal guaranteed speed is 100Mbits and that's not possible with the 2.5Gbits / 32.