The X125t is a noticeably stronger, smoother motor, as strong or stronger than the Rotax in the midrange and matching the X30 in top end, so it’s the best of both worlds. I’ve found myself overtaking Rotax’s on parts of the track where they used to just drive away from me, while still enjoying that IAME-like extra top end.
I only have one race under my belt on the X125t, so I’m still learning to tune it. My motor seemed to have a overly-drastic (and very unforgiving) power drop when off pipe, but I suspect that was partly due to a jetting issue, my unfamiliarity with the motor, and (admittedly) my not exactly being a national-caliber driver (I’ve got a new chassis and I’m learning that at the same time). So the X30 might have a low-rpm advantage over the X125t like it does over the Rotax, but I can’t be sure at this point.
I like the simplified ignition system on the X125t, but there’s a trade off as it doesn’t charge the battery like the IAME selectra system does. On the other hand, the motor seems to start very easily so I had surprisingly little battery drain over the course of the day and charging wasn’t an issue. I still bought a trickle charger for overnight recharges though, which I never had to worry about when running IAME motors.
So I’ve got a lot to learn but I’m not regretting my purchase. If the X125t is legal in your series it’s the clear choice in my book, especially since Italian Motors is running a trade-in program.
Update March 1, 2015: After some practice and another race I’ve confirmed that the power drop I mentioned earlier is at least partly due to learning to jet the motor correctly. It does not pull as smoothly from low rpm as an IAME, but the Leopard driver’s trick of the pole sitter using a very slow formation pace (which puts the Rotax rpm underneath the power valve) does not work when used against the X125, or at least not much, so the power band is not falling off a cliff, as I had feared in my prior post.