I don't have any experience with Magnum, but I own a Saito 91, which I love. As far as I know, the Magnums run fine and are basically OS clones. You really answered the question yourself when you listed the weights in your post. The Magnum 70 weighs 4 ounces more than the Saito 82 and 5 oz more than the Saito 72. Saitos are generally lighter than other 4strokes of similar displacement and may have a little higher quality than Magnum. BTW, you ought to be able to find the Saito 82 for less than $254.

I am strongly considering a Magnum 70FS for my next engine, so I'll be interested to see what others say.

-Scott