Download speed of ~51Mbps is plenty fast enough for any game downloads - something is not configured correctly on the xbox or it is misreporting the speeds.
That said.... There are lots of options for improving wifi speeds which we can go into.... however, before trying them - can you easily run an ethernet cable from the Hub to the bedroom - if so that affords the best solution. Or this might be good - but others on here dont like them...
My lad is a serious internet gamer who thinks wifi is the work of Satan and should never be used for gaming. Ethernet cabling your devices is always the best way to go, but running cable to his room was problematic. So he uses a pair of Solwise AC1200 powerline adapters. His PC/Xbox/PS3 can now all be "wired" - with short Cat6 cables – back to the wireless router downstairs and he gets a solid 60-70Mbps on our V200 package - he hasn't complained once in years!
Worth considering whether that will work for your house on your mains circuits, the two circuits must go through the same consumer unit/fuse box (most do) and be free of any "noise". You can also add a wifi access point alongside to boost that up there as well. Or some PA’s have built in wifi too - look at the TP-Link offerings.
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.