I guess you haven't deleted the .bin files between testing...
cgminer-2.3.6 and cgminer-2.4.0 located in different folders. I copied config file from 2.3.6 to 2.4.0 and received result 418Mh/s
Did you delete the .bin files in the 2.3.6 directory after upgrading your driver+sdk?
No. Here are the contents of my folders:
This is what I'm trying to say.. .that has been said many times and is in the FAQ. If you run cgminer, it caches the binary built from the SDK installed the very first time you run it, and then even if you upgrade driver+SDK, it still runs like the old SDK. However if you install a new cgminer, there are no cached .bin files (see the .bin files in each folder), so it generates a new .bin file from the current SDK installed. The only way to compare versions 2.3.6 and 2.4.0 with your current installation of driver+SDK combination is to delete the .bin files from both of them and start them both again.