If you want a full recommendation by one user, here comes:

1. Everything you can download from http://www.tesnexus.com/modules/members/index.php?id=1394013.
2. Install the LOD and any parts Ampol?s textures wont cover from CorePC?s http://www.tesnexus.com/downloads/file.php?id=18677 pack.
3. See the section about "Improved trees and flora" http://devnull.sweetdanger.net/totoworld.html and get everything related to it.
Maybe download some other ruins/dungeon/town packs from TOTO?
In any CASE, make the Ampol?s textures into an OMOD you activate last, if you want all those in any case, like I do. You can, for example, activate all the Vibrant packs before that, to have a base install of good looking textures that wont destroy your performance. Note that Ampol?s textures are also a very nice compromise in size, "only" 1024x1024, so you can throw those in pretty much without worries as well.
Activate all those "trees and flora" etc after vibrant textures (or QTP3, should you consider that as the base install? But note that it requires a lot of vram and wont give you LOD...), and see if you handle it, some of the textures are very high res. But very good looking as well. Then throw in Ampol?s stuff last, to have all the goodness from it.