I have the Fantom .15FR in my T-Maxx. I have been running if for almost a year now, and it does really well. It provides great top speed, and when properly geared, awesome low-end torque. I am geared for the low-end torque and still managed to post some speeds greater than 35mph.
I have not had a chance to run it against the new 2.5 (the one opportunity I had, the fellow broke the front end off his truck before I could get mine started). I have run with Pirata's .21 and held my own.
I am currently looking for something with more power. This is not saying that the Fantom .15 is underpowered; its just that my T-Maxx is getting heavier and heavier as I upgrade to more and more metal...I may try one of 3maxxman's mods to drop a .21 or larger into the standard chassis (but that is a tale for another time).
Anyway, I think the Fantom is a great investment and will give you what you need. Their customer service is also top notch.
If you really want more information, try a search on this site. You will find several threads on the Fantom and quite a crowd of Fantom users (not as large as the OS crowd but a crowd none-the-less).