@Skyspish not sure what your issue is but in general Sky like any other ISP can only guarantee the speed to your router. That speed is pretty much the same whatever iSP you choose selling the same product as with copper lines its set by the length of your phone line or if you have fibre to your home by the speed you buy.
The speeds you get at your devices will vary especially if you use wifi to connect as the layout and construction of your home comes into play. Wifi dignals are also subject to interference which is very common in flats where your neighbours networks can be within range.
If you want to play games on a Xbox it is highly recommended to use an ethernet cable not because internet gaming needs a lot of bandwidth but because wifi is subject to higher jitter due to interference. Adding a booster can help,extend the range of a router but is not a magic solution it wont help,if interferencecis the issue. If you want high speed wifi through out a home you often need to invest in your own kit rather than relying on what Sky give away for free.
If you would like help to improve your speeds then post your hub's connection stats see here Find your Sky Broadband router statistics
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
