You could use the Siper Tigre .45 on the trainer but it is a bit much in my opinion. I have the ST. 45 with a Macs muffler on my Sig SE and it flat out screams; a nice engien for that plane. I had a Tower trainer a while back with a .46 LA. It was more than enough. As for your .40, it definitely won't have tons of power to spare but what do you really need for a trainer anyway? The only downside to the .40 is fewer options to put it in later. Just my opinion of course.