Well, I don't have a1GB line. Just a 500MB for testing on a friends line. I own the ER-X and the same hardware as R7800 based device NBG6817. So I cannot confirm those numbers by myself respectively only the own perception that they reach the 500 MB on WAN. For the NBG6817 I saw only 400 MB with OpenWrt. While I got ~ 500 with stock firmware.
But there are clips to reach those performance numbers. For the ER-X you have to enable hardware offload and drop any bandwidth management (like sqm) on the router. You can reach ~900 MB on the ER-X based on that what you can find about the device in www.
The same would apply (I don't know) to the Linksys device. Hardware offload is not available for most devices! The Linksys device should perform slightly better then the ER-X.
There are some threads on the forum about the performance of this devices.
The differece between the R7800 and the 1900acs is probably (I can guess only) the CPU and the missing hardware offload feature on the r7800. Most likely the last one only.
But there are other ppl. here on the forum with deeper knowledge then me which could provide more about this.
For the GL-MV1000 I cannot say anything. Its a newer device (others above are ~5 years+ old) and specs are looking better. But be aware the Chipset must support hardware offloading and OpenWrt must support it as well!