Moving from cable to full fibre alone will help in online gaming due to lower latencies. Speeds don't matter much for that.
Is the FTTP from VM as well or another provider? Some networks like Openreach will have much lower upload speeds compared to download, while most altnets are symmetrical. Streaming prefers good upload speeds and last I checked with VM 350 at least, upload was limited to ~35mb odd. Either way it will still be more than enough when streaming to Twitch/YT/etc.