It's not really features vs performance. I don't know where you are based, but here in Europe ISPs must (I think?) put the router into bridge mode upon your req

It's not really features vs performance. I don't know where you are based, but here in Europe ISPs must (I think?) put the router into bridge mode upon your request, from which point you can use whatever you want and the box from ISP acts mostly as a modem/media converter. I was even able to cut out this part by using an SFP GPON module I found! Regarding speeds, it depends on what you are working with. Basically anything can do 100Mbit, most basic consumer gear seems to top out at around ~300Mbit and if you want to go higher, you need more powerful ARM SBCs or x86 based routers.