Good FPS to cap at?

G'day. Currently running GW2 on a ryzen 5700x, RTX 4070 TI Super, 32gb ram, nvme SSD and monitor is 1440p 144hz with gsync.

Most of the time my frames are well above 144fps But in WvW and large metas they drop to around 40. I still find the game quite playable at 40. I'm thinking about setting a FPS cap at maybe 60 or 80. Primarily to take a bit of load off the computer in an attempt to reduce temperatures.