As already said, your ‘line’ and the equipment that delivers broadband will be the same regardless of staying with BT or moving to someone else, so the speed you get will remain the same if you move or if you stay, the figures you are looking at are ( IMHO ) not very informative, your predicated speed can be gauged by the BTw checker , compare that to your current router statistics which will show what your connection rate is and the maximum attainable rate,
The figures you quote are not some sort of cap, if your line can sync at ( for example ) 36Mb and the minimum speed guarantee is 25Mb , they don’t hold back your speed to that…it’s just a speed at which should you fall below it, the ISP has to get you back to that minimum or allow you to leave penalty free, the supposed ‘check’ Sk* performed is nothing more than BS, how can they check anything apart from the wholesale data.
Connection speed is going to be pretty much the same regardless of the provider , providing the same band of service is purchased , 40,55 or 80Mb , it’s the line length and quality ( which is the same regardless of provider ) that dictates how close to those figures you get , throughput is different as that could vary depending on how much bandwidth the individual ISP has available, a general rule of thumb though , is if a provider is ‘cheap’ , one way to be ‘cheap’ is to skimp on the backhaul bandwidth.
If your individual line should perform better, you may have a fault or your home setup may not be optimised, posting your router stats and info from the checker may help in that regard.
https://www.broadbandchecker.btwholesale.com/#/ADSL
