Good sense of feel. http://dbzeta.net/topic/11177526/1/
I still have the same difference between his forms as I did before fnf and I consider SSJGSS around a 2x (with an extremely powerful God tier base ofc)
I tend to have the difference between the forms greater than they were in the Freeza arc due to everyone's flabbergasted reaction to Freeza transforming to his true form (when they experienced all his powers save Kuririn, Tenshinhan, etc.). I've not done concrete numbers yet, though.
1st Form - Much Weaker than SSJ3 Goku (more than twice actually)
2nd Form - A bit stronger than SSJ3 Goku
3rd Form - Inbetween SSJ and SSJ2 Gotenks
4th Form - Super Vegetto Level
Based on statements in the movie 1st form Freeza could easily be any level higher than "a completely different level" than Gohan and Piccolo. I'm just going to go ahead and place him at the following:
1st Form : around Super Boo
2nd Form : weaker than Super Vegetto
3rd Form : somewhere between SSj and 2 Vegetto
4th Form (50%) :around SSj3 Gogeta (BoG) or weaker
4th Form (70%) : around SSj4 Goku (Super 17 Arc)
4th Form (100%) : around SSj3 Vegetto (BoG) or weaker