I have a 751ui-2HnD and was using it as one half of a wireless bridge. I found that it was incredibly slow, not so much with traffic but with general winbox and terminal. It would take over 10 minutes after it booted before I could login and then winbox would keep dropping out. After a while it would become more stable. I tried upgrading to 7.3.1 but that was unusable and went into a reboot loop, I was lucky to be able to connect for long enough to roll it back. It's now running ok in the same network chain once I removed it from the wireless bridge but still pretty slow. It seems to sit at 100% a lot. Traffic demands are a single user with a max 30 mbit internet but it is problematic even with no traffic.
Anyway, my question is, is this what I can expect from the 751ui? Is it just too old or is there a fault? I've read about checking flash with /sys check-disk but it doesn't have that option. Anything under /disk doesn't seem to help and I have done a check installation.