For resolution open your skyrimprefs.ini and find the following
and input your resolution. Save the file and voila.
As for performance increase, there are many things to do to get a bit more. I would never recommend to disable the SSAO since it does provide so much in terms of visual. You can disable reflection and get a bit more that way, its effects are more subtle overall, and you most likely will not miss it.
However since you already have the ini files open then make sure that your shadow resolutions do not exceed 2048, or just set them all to 1024
In skyrim.ini under GRASS
Put in this
It will lower the grass density and in effect make sure you get a bit more fps there. The higher you go the less grass and vice versa. You can find the sweetspot for you.
Other then that, you can disable the Depth of Field effect if you do not care about it and get a bit more there as well. You do this by pressing shift + enter while ingame to get the ENB GUI up. Then on the left you will find a drop down menu where it says EFFECTS, and there Depth of Field. Also this is where you can disable reflection.
Hope that helps ya out!