It is not like that, the ipsw created by pwnagetool still has the actual 05.11.07 baseband as a file in the restore ramdisk. However the option to update the baseband during the restore is turned off in a config file contained on the ramdisk. So in effect you stay on the baseband you had before you restored. THis should be 04.26.08

I downloaded that ipsw you mentioned but have not been able to open up the ramdisk yet, i must have the wrong decryption keys or something.