I hope that 158s are retained on theh Cardiff - Portsmouth service. In my view the use of 165/6 with the 3 + 2 seating would be a retrograde step on a long distance service. Further the lack inter-unit gangways could also cause problems with localised overcrowding
I think someone mentioned earlier in the thread that the 3+2 seating would be modified when these units move west. The 158's are desperately short on leg room though, so be careful what you wish for!
I think the ideal solution for this sort of route would be something like
ATW▸ 's class 175 - airconditioned, good top speed and fabulous amount of legroom for a modern train - not sure if they could do an interior refit on the 16x's to provide the sort of legroom found in the 175's (I suspect the number of door openings might be an issue), but some thought needs to be put in to this as the current 3+2 bay seating isn't the best suited to mid-distance routes imo.