It would be much easier to tell with a screenshot like #2, but with the visleafs showing so we can see where the cuts are.
But I think you can still optimize more. A screenshot can be hard to tell, not as good as flying around first hand.
Anyway. Those nodraw brushes sticking up could go. All they are doing is cutting up a bunch more leafs. And more leafs is probably worse performance than any culling that might be happening behind them.
I also think the building on the left could be fully func_detailed. The reason is there is only a slim chance that it is blocking view of anything anyway whether inside or out.
And that angled nodraw on the left, I'd just make it flush flat so you don't get weird cuts stemming off of it.
Take Gpit for an example. The entire A, B and C areas are func_detailed. The ONLY optimizing is in the tunnels between those areas. And they run fine on 32 man servers.
Better to have fewer leafs than anything imo.
And as said above, clusters speed compile time, but don't really optimize in game. (though they could make it worse by grouping too many leafs together and making more stuff render around corners and such).
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I'm wondering about that round roof and the angled next to it. Do you see those shapes inside? If not put a flat brush up top inside and that'll help seal that area a lot.
At least put an area portal, but with the weird L bend, if the portal is on one plane it might not work properly. So maybe put the angled one down a bit and seperate those rooms with a wall or something (at least a partial wall high up). (maybe there is a wall inside)
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I'd be happy to take a look on tues night/wed also if you pm my a vmf link.