Three Portsmouth diagrams are using 3-165s today where they'd have previously used a 166. While similar, I personally (and I know others do too,
@cactustwirly will no doubt back me up here) find the 166 to have a far more superior environment, with more 2+2 areas including double the former first class seating (and those sections have tables), half tables and a sort of half vestibule situation unlike the 165s. You don't have a single thing to rest a coffee or laptop on with a 165. I do hope some distinguishing diagrams will be created to keep 3-165 and 166 on shorter and longer distance Turbo diagrams respectively. Perhaps when GWR are in a better position to organise their stock.
I was actually one of the few forumers not to mind the conversion of most services (planned at one point to be all, now it's been scaled back to about a 50/50 split) from 158 to 166, as I found the 166 to be a good compromise between comfort and the need for more capacity around major commuting hubs, but I think the 3-165 is a bit too far. Maybe one every now and then is fair enough as GWR's fleet is troublesome and difficult, but today only two 166s are on the route.