Magnum/ASP, TT, OS, Irvine, GMS and Tower 46s all make right about the same power. They'll all run within 2-300 rpm of each other given the same prop (power difference is negligable). We've tested many different varieties at our club and there's definitely no clear winner, unless there's a displacement advantage (such as the OS50SX or Irvine 53 which will both outpower a BB 46). In terms of reliability, it was true that OS engines (made in Japan) were more reliable, but the Taiwan and Chinese companies have caught up at a dramatic pace. I've never seen a newer (less than 3 years old) model from any manufacturer run unreliably unless the owner doesn't know how to tune the engine. My order of preference for this size motor would be TT Pro-46 (at $70, it's the deal of the bunch), Irvine 53 (at $99, it'll outrun any 46), the newer Magnum/ASP XLS46 (at $80, sure looks like a 46FX), OS46FX (at $120, the most expensive of the bunch), and last the Tower/GMS 46 (at $75 a good buy, I've heard they leak air through their bearings making them hard to stop unless the fuel line is pulled, but a local flyer has one and it runs and stops like a champ)... In terms of engine design, I personally don't like remote needle valves (they might be safer but IMHO, the closer the better for fuel delivery), but it looks as if this is the way that OS and Magnum/ASP are going. Also look for fins that are more squared-off rather than rounded. These have been designed for maximum cooling. That being said, if you build your LT-40 light or maybe consider an LT-25 (sub 5lb with engine for an LT-40 or sub 4lb for the LT-45), you may just want to look into a hiperf 32-39 engine such as the TT Pro-36, Irvine 39, or LEO/Megatech 37. Or if you're on a budget, try the TT GP-42. These engines all produce near BB 40 power but weigh significantly lighter (10-13oz with muffler as opposed to 16+oz for the 46s) and drink less fuel. Plus their perfect for that Magic or Uproar/Dazzler that you'll be getting in the future