The most powerful .46 size engine is going to be a .52 or .53. As has been said, most bang for the buck is a Magnum .52XLS. Some people may like the Irvine more, but at $139 vs $99 it is a good bit more costly.

The problem with Rossi engines has always been weight. If weight doesn't matter, they are good, powerful engines, but for a fun fly type plane where weight counts, they may not be a good choice.

Practically speaking, there is probably the same difference in individual engines of the same brand as there is for different brands. I own several different types and they are all close. You will not be disappointed in an OS, Thunder Tiger or Magnum. All are top-of-the-line engines with good warranties. I also own, or have owned, Tower, MVVS, GMS, Rossi, Fox & K&B. They have all run well for me.

With the web exposing any and all flaws, I would venture to say that all .46-size engines, the most popular size, are pretty much equal. Since I have many years running model engines, since 1950, I find I can try them all and not have any problems. My new OS .46AX is a sweetheart, easy to run and powerful. If you have read my posts on the web before, you'll know I do not push OS, but the new AX is a little gem. It's not the most powerful, but it runs great in all rpm ranges. My Magnum .52XLS, and I have 2, is a few more hunderd rpm faster, but is a little trickier in the mid-range. The GMS is a little slower, but runs well. My TT .46Pro is powerful and has run well for years. I'd buy a couple more if I didn't just want to experiment around. The Tower I have I got when they first came out. It still runs well, but is showing its age. I have it on a float plane.

All of these engines will go 700-800 rom faster with a Tower muffler. I tried one on the AX, then on the Mag and ended up ordering 6 of them. $15 bucks for 800 rpm-I guess so.