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