Is a new bike. Sirrus X5.0
Has a 40T single ring on the front and a Shimano SLX M7100, SGS, 12-speed rear Derailleur. The cassette on the rear is 11-51t.
What would be the easiest way to improve speed?
Change the cassette? If yes, which ratios?
And would a large cage rear derailleur accommodate that cassette?