FJ is much more in your face than Mummy. Mummy is a coaster with some speed. FJ is a vehicle on the end of a kuka arm being tossed around. It is hard to compare because the intensity is very different between the two.
Mummy's intensity comes from the coaster elements. FJ's intensity comes from your surroundings being so close and in your face. I don't find the actual ride itself to be intense...it does move you around but in a smooth way.
I am not a fan of roller coasters.... and I love the Mummy. There are drops....but not big drops. The ride goes fast....but not that fast. The Forbidden Journey is completely different, and not a roller coaster. It is a simulator ride that moves. The ride goes right, left, dips a bit, but does not go upside down. The most is does is have you laying on your back for a moment or two. The reason you feel things is all sensory. By watching the screen, you feel like you are flying. This is one ride that if you didn't like it, you could close your eyes, and all you would feel is a relatively slow movement of the vehicle. My husband doesn't go on many rides.....and even he has been on FJ four times.
My DD10 went on them both at 7. She was OK on Forbidden Journey but Mummy was the only ride she hated. She has some sound sensitivity and she said it was too loud and it made her cry. (The only ride to ever do so.)
I, on the other hand, am a big chicken about certain things but OK on coasters. I liked Mummy just fine, but FJ did me in. I just couldn't handle all the in your face stuff - especially the spiders! Even with my eyes closed I could still hear their clicking. If those restraints hadn't been holding me in, I think I would have run away. I bawled like a baby after.
The first time we went on the Mummy, we didn't realize there was a roller coaster portion. So my son had his first roller coaster experience unwittingly . Got him one of those "I survived the Mummy" t-shirts as a reward. Now it is one of his favorite rides. I like it, but the fire part kind of freaks me out.
I think Mummy is certainly more intense as a ride, but FBJ takes more of a physical toll on you. If it didn't take so long to get through the line, there'd be no way I could even ride it twice in a row. Three times is out of the question. With Mummy, I can pretty much ride that over and over until I get bored.