A mix of Nightingale (as I don't like th enchantments really) and DB.
Or, you can do the Ancient Shrouded armor full set or the Blackguard's Armor. Both of these can reach the armor cap of 567 just fine.
Ancient Shrouded DB armor is obtained obviously through the DB questline, but when you do the dark elf's quest (forgot her name, she's in the robes) if you do it the "extra" good way, she will give you "Olava's Token." Go ahead and do that, and the location will be revealed. However, if you don't want to join the DB there is a way of getting it as well, just let me know if you need the info (so I don't have to explain it if not need be).
The Blackguard's armor is a better version of both Thieve's Guild armor and Guildmaster's armor. In look, it is very similar, it's black. But the enchatnments are better and the armor rating is as well. This can only be obtained by having the Dragonborn DLC. Join the TG fully, then when you travel to Solstheim (however it's spelled), when the boat lands, go to the left and find the blacksmith Glover Mallory. You'll have to do a mini quest and then he gives you a key to his basement containing this armor and other good stuff.
I wish you could find unenchanted versions of these things, but I've tried everything. There is worn shrouded armor from DB, but it can't be enchanted or improved, so don't see the point in that. But I agree with you on all of the other armors, they don't say thief or assassin to me. So this is the track I've always gone.