Hi, yes, "fine" is relative.
I can't exactly remember the FPS but when i took care in the base i guess it was between 20-30 FPS at late-game. It was very playable and as i said, i only got heavy lags when i messed up my base and had too many open tasks.
My old PC is already disassembled. So, i am sorry, can't do the Brenchamrk anymore but would had been interesting.
And sure, on my "new" computer, i5, ocatcore , 32 GB Ram but still gforce 860, ONI runs of course a lot smoother. - but far away from lags when i follow the rules.
And i am not sure if pathfinding is the only reason, maybe too many flashing icons also contribute.. but i dont know, i have not tested a lot on this issue.