Have you tried raising the "uExterior Cell Buffer" value in the ini file WITHOUT changing the "Ugridstoload" value?
I had CTD/freezes outdoors with Ugridstoload=7, uExterior Cell Buffer=64, but everything seems fine with Ugridstoload=7, uExterior Cell Buffer=100
Maybe you could try Ugridstoload=5, uExterior Cell Buffer=64
On a side note: at first I reverted to the standard values of 5/36, and didn't suffer any CTD, but even with STEP the game looked pretty ugly imho, or at least non immersive at all with all the buildings, trees, textures, etc. popping out every 10 seconds or so :(
I would advise anyone unable to run STEP with a Ugridstoload value of 7 or 9 to desinstall some of the biggest texture mods (or downgrade them to medium res version, or try Texture Optimizer) rather than returning to the standard value of Ugridstoload=5.