Is the TP-Link 1043ND v.1.x able to use the full 250mbit downlink from WAN to LAN port? I am asking, because I only get 110mbit but the router has 5x gigabit ports?! Wouldnt that be sufficient to pass through 250mbits?
Traffic between LAN ports remains internal to the hardware switch of your router, the router's CPU never gets to see the traffic and you achieve full 1 GBit/s line speed. Whenever the CPU needs to do something with the traffic, such as routing, NAT, firewall, it needs to leave the switch, through the CPU port of the switch (twice, LAN --> CPU --> WAN, the TL-WR1043NDv1 only has a single CPU port and a 6 port switch, which distinguishes between WAN and LAN via VLAN tagging) and then the slow 400 MHz single-core mips 24Kc CPU is tasked with operating on the packets, this is a bottleneck (several, actually).
Keep in mind, your device has been released about 9 years ago, when 16-25 MBit/s WAN links were considered top end, the device was designed accordingly. Even today entry-level devices won't provide you with much more than ~150 MBit/s routing performance, the faster you go, the faster your router needs become - and ARM based multi-core CPUs in the 1-2.5 GHz range are increasingly replacing the <900 mips targets.