Textures: you know I don't think you need 'em that big. I use UDK and whenever I need something to look nicer or more detailed, I just add a fat-layered "detail texture" (about 30 layers of stacked normal maps - anything that gives a chunky/grainy look) to the basic normal map and the bump map too. Maybe tile up the texture. Ppl usually do this in this engine. It's a cool trick. Saves you the mess with resizing and getting new textures.
I don't know if it's possible in the iwengine, or whether it even uses normal maps instead of height maps. Maybe you've been doing this all the time. I just thought I mention it. Might even be of help.
http://www.cgtextures.com/content.php?a ... =normalmap
This shows off the perfectly looking normal map - to which you add another one, created with the same technique, but from a different texture.
Edit: before adding the 2 normal maps, you need to "erase" the blue color information from one, and replace it with 0 (zero) value. If the engine can do it, it's good, 'cause it might be difficult or impossible to do that just in photoshop.
Oh and I highly recommend checking other stuff on that site as well. There are more tutorials with nice tricks(recoloring and complex tiling). There are perfect textures as well, even for 360° sky domes (HDR versions also avalaible).