I am running OpenWRT 15.05.1 on a Buffalo WZR-HP-G300NH, and am getting a max download (through speedtest) of 175Mbps. The admittedly pretty old 400Mhz CPU gets maxed out at 100% during the test.
I would like to try LEDE, but is there is any reason to think LEDE would give me higher download speeds than OpenWRT 15.05.1 on this router?
That sounds pretty much like the hardware maximum, limited by the CPU speed, I wouldn't expect significant changes* in that regard.
*) given that you are constantly hitting the CPU limit, even small differences might actually be noticable, but in the absence of major driver changes/ additions (unlikely for devices of that vintage) the general throughput is likely to stay roughly similar. With software tending to get slightly larger over time, thereby taxing the CPU/ RAM more than before, an already CPU limited I/O throughput might actually slightly regress over time with newer versions.
Thanks for the reply, that is what I figured. My ISP gives me 250Mbps, so I am looking for ways to squeeze every bit of performance out of this old router. Although, I could just get a new one.
I'm running LEDE Reboot SNAPSHOT r2695-c9c68c7 on a TP-Link TL-WR1043ND v1 with 400Mhz CPU.
My ISP gives me 200Mbps and I'm happy with the speedtests:
If you don't need it disabling mss-fix on WAN will help a bit in terms of performance.
@IronicSven Good to know. You have given me an excuse to start tinkering with LEDE. 
@diizzy Thanks, I'll give it a try. Is this the mtu_fix option?
Another thing you can do is overclock the cpu, AR9132 maxes out at 430MHZ
Tried on a few TL-WR1043NDv1 & running @ 430MHZ for more than a year
Take a backup of your uboot
dd if=/dev/mtd0 of=/tmp/bootloader.bin
Then find the values that determines clockspeed
Make the changes then flash and overwrite the bootloader
why would you overclock a router's SoC? In best practice, overclocking a router is not recommended, it will just bring more issues than not.
you better just buy a newer router that matches your bandwidth needs.
Like what?
I didn't say to overclock to any arbitrary value.
430MHZ is a clockspeed I tested on my routers for a a few months.
If you try any value higher @440MHZ you will get kernel crash occasional reboots in a month, go higher and your router will go into a bootloop crash.
If you didn't test or experiment and conclude that it is "bad" because it kills a kitten then I suggest you shouldn't even bother touching LEDE and stick to your good vendor shipped firmware.
FYI, my WZR-HP-AG300H on LEDE r2818. SpeedTest results
Gb LAN:
302 MB. My Plan is max out at this speed (Tested on LEDE WRT1900ACS)
Wireless on Speedtest on iPhone 7
138 MB - N 40MHz Channel 149 5.745 Ghz WPA2-PSK AES
49 MB - N 20 MHz Channel 11 2.462 GHz WPA2-PSK AES
Never got this speed previously on ddwrt openwrt and stock firmware.
Buffalo WZR-HP-AG300H
Atheros AR7161 452.19 MHz, Gb/802.11abgn 2.4G + 5G
Well, I gave LEDE a try. I was getting 175Mbps download with OpenWRT 15.05.1. With today's snapshot of LEDE I am hitting 212Mbps. Not a bad boost in speed. With my ISP maxing at 250, not much need to upgrade my router. Nice work!