I am not sure a stainless would benefit you much on a 40 hp motor. the big benefit of stainless is that it doesn't flex under power. There are some benefits realized as manufacturers of props can get a little more creative in their design with the stronger stainless, but I am not convinced that you will be able to see the difference with a 40 hp motor.
You will not be able to trim your motor all the way out. Depending on you speed, prop, and the depth of your motor, you will be able to trim up more or less. Think of your trim as fine tuning. It is the last thing to worry about when setting up your boat.
First, make sure that your motor is at the correct height. When your boat is on plane, your anti ventilation plate should be right at the water's surface. This is the big plate at the bottom of your leg. The last one before the prop. You don't have to be at at the absolut top speed of your boat just well onto plane. If this plate is below the surface, raise your motor up a notch and check again.
FWIW it is very rare that you would have to lower your motor. Lowering your motor will lower your RPM and lower your speed as you are dragging more leg in the water. Also, most boats are set up with the motor too low. A low motor prevents your motor from ventilating/blowing out on turns. If your motor is set up properly, you should have to trim down to make turns without blowing out. Many people see this as undesireable, but think of it this way; If you have trimmed(fine tuned) your motor to the limit when going straight, why do you think this would be a good setting when you are turning.
Once you have your motor at the right height, you need to size your prop correctly. Load up your boat with a typical load that you would have in everyday use. If you always have a 40lb tackle box, a 20lb cooler, and a 250lb buddy, make sure you have them in your boat when doing your test.
Bring your boat to wide open throttle(WOT) and start to trim up your motor. when it ventilates, trim it down a hair until it stops. Read your RPM and your speed. Preferable use a GPS for speed. You need your RPM to be at the top of the Manufacturers recommended WOT range. If your RPM are low, go to a lower pitched prop. Vice Versa if your RPMs are high. You will usually gain/lose around 200RPM for each inch of pitch. Once you have the WOT RPM correct, it is time for fishing.
FWIW, my dealer assured me that the setup was correct on my boat. I ended up raising the motor one hole and going down 2" in pitch. I gained about 700 RPM at WOT and didn't lose any top end.
my boat: Alumacraft Trophy 185 w/ 150hp etec
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