This is an example of what happens with different capacitance. You see that the treble gets boosted and then quickly rolls off (i.e. the level decreases compared to other frequencies).
If you google “Hagtech loading” you’ll find a page with a nice calculator that will show this (approx.) where this will happen for a cart with a certain capacitance. AT luckily lists all required specs for their carts. Please note that the capacitance your cart “sees” includes the cabling as well. Likely 20-30pF for the tonarm cables, and another 60-70 or more for the actual phono cable. So say another 100pF on top of your phono stages spec.
To compare phono stages it would make more sense to get some high capacitance cabling to use with the Rega and keep using the same cart. That will also allow you to experiment with the audible difference for you between high and low capacitance. If you then prefer the XS3 you can see if you can find a cart that’s more suitable for the high input capacitance. If you prefer the Rega keep using the cart you have.
No, it’s an MM cart. Resistance for MM is standardised at 47k, I don’t know of a single phono stage that even allows configuring that.