for 300Mb/s and just NAT only, the tp link that TM give will handle that. If you want a fully featured router with such software processing speeds heres some you can look at.
Newer ASUS like the AC86P with improved ARM CPUs
quad core marvell based routers like some of linksys
64 bit based quad core ARM based routers
On the non consumer but small user segment (at the lower pricing tier):
Mikrotik RB750gr3 or better
Ubiquiti ERPRO or better (The newer routers with their newer CPU might be better)
x86 based like pfsense on intel atom (i would not use AMD equivalent of intel ATOM, but even bulldozer based arch can be used) with a used quad port intel server NIC or a fully featured linux OS as a server
may be other options here
i dont have any exact models to recommend, but at least you can search for such routers. There are other routers some would consider overkill, like mine even for 800Mb/s TM but some of us end up with very overkill stuff. You can scroll back a couple pages to see what i use.
I remember using pfsense during my Final project. it was fun yet a bit complicated(but not as routeros) . You can use any recycle pc with min 2 NIC card to convert into dekstop router. I dont recommend mikrotik for all user as its a bit hard to understand at first, and you need some sort of knowledge in networking in order to fully utilize your router.