That's weird, I always thought the contrary : TriX as a contrasty film and FP4+ as a soft film, nevermind. I shot it as 100ASA, but I don't have the time I used with me now...I also use dichromate bleach so maybe this is why our results are different ?
In super 8 I'm using reloadable cartridges "kaccema" so I only buy film in bulk. It's much cheaper than commercial cartridges, here in Europe. So Adox maybe some day...Up to now I was using Orwo UN54, and think about trying the Fomapan. But I didn't really succeed at getting good contrast (that Rodinal must be the reason!) so I might be buying another roll of the Orwo to fix it up, don't know yet
Oh and btw, the TriX super 8 stock changed some years ago (5 maybe?) so perhaps that's why your results are different