ORIGINAL: WMB
My 4*40 currently has a Saito 45. Definately not overpowered, nice gentle flier. Saw another fly with the Magnum 52 and it did well. You may want to consider how/if this engine will be used in the future. If you went with Saito 72/82, you won't lack for power and your choice of future planes is wide open. In comparison, the 45 is more limited as to working well in other planes, slightly heavy compared to power output. I think the 56 or 62 would be a whole lot of fun.
Have fun, MikeB
My thoughts exactly. It will fly with well with the 52 but a 72 sized 4 stroke gives you a lot more options in the future and will be fine on the 4*40. Also for puttin around the sky unless you are wanting a higher performance 4 stroke for later down the road I would go with one of the more economical 4 strokes. I really like the magnums. The run great and are a great bargain. They also run great on 5%.