There are/have been quite a few 4 stroke .40s made in the last 25 or so years. Here is an approximate chronological order:
The earliest that I know of is the ENYA .40 open rocker - quite powerful but heavy. Equivalent to an FP .40 but much heavier.
Then they made a closed rocker version - rare, as it was imported in very small numbers - I have no experience with it.
Original SAITO .40 - about the same size as the .50 - a nice smooth engine but power-to-weight leaves something to be desired. Makes about the power of a good Fox .35 at twice the weight!
OS non-surpass .40: a wonderful, user friendly smooth, powerful and economical engine. If you enjoy sport and occasional competition flying, this may be the only engine you'll ever need. Put one on a profile Cardinal and you might just realize the perfect engine/plane combination for just about everything. The engine is so well set up and balanced that it will probably never wear out. Perfect fuel draw, no muffler needed, 11-7 prop, two ounces of fuel for the pattern. I have NEVER had an engine that runs more uniformly. They usually go for peanuts at flea markets. I would estimate that it makes the power of an FP .40.
(I can't remember the details but a while back I sold one to a gent in St. Louis - as I recall, he was told by a self-declared expert that he bought the wrong engine. I hope he reads this and realizes that he has a real gem of an engine.)
Surpass .40 - unbelievable power. Nasty, as it hates props and lets you know by constantly throwing them at you - I make special prop washers for this beast and they do the job. I have one on my 59 ounce Euclid II and it about pulls my arm off. Fortunately, an extra head gasket tames it nicely. One of the more thirsty 4 stroke engines. Some of the early ones suffered from improperly hardened exhaust valve which are fortunately very easy to replace. Probably makes the power of an ST .46.
SAITO .40A - a real sweetheart of an engine that has actually replaced some piped .40s with great results. A tad bigger than the .30.
Regarding weight, I'm not positive but I believe it's close to that of the Surpass .40. I will check as soon as possible. Powerwise, it approaches that of the Surpass .40 but not quite up to it.
This is all based on my experience - I hope it helps.
Bob Z.