OP,
I don't know what the price difference is between the 300 and the 425 but, I can tell you this, while you or your wife may be a bit skiddish about higher speeds, if and when you might need those higher speeds for whatever reason, you're gonna be darn glad you got that higher HP motor. No one says you have to use that higher HP ALL the time. But it's really nice to have upon request. Our Benny is a 2014 25RCL and it came with the Yamaha 350 4-stroke FI. 5.3L engine. That boat is a big boat and, that engine get's it on plane in about one boat length. While about 97% of our boat speed hovers between 25 and 35 mph, with just the two of us (and our little mini Schnauzer) on board, a half tank of fuel (57 gallon tank) and, both of the dual biminies are up and zipped together, I can achieve 50.5 mph on it.
But, that's WOT or, wide open throttle and, right around 6,500 rpms. I don't run that fast very often, about once every couple of times out on the lake and even then, for only about a mile. I can watch the fuel gauge go down as I run that fast. There is no need to run that fast. I'm not needing to impress anyone. But, one of the really good points about having a larger engine is, when you load that boat with more than just the two of you, AND some kids or a few more adults, the larger engine just doesn't work very hard at achieving plane and, keeping it at the speed you're requesting. Whereas, the smaller engine will work for sure but, it's working just a bit harder for the same purpose's. It's a choice thing. I know if it were me and, while the higher HP engine might give me a bit of sticker shock, knowing what I know and have experienced the benefits of higher HP, I'd opt for the higher one in a heartbeat.
And as has been stated, your resale will also be up quite a bit as you'll attract more potential buyers when they know you have a higher HP engine. Good luck.
Scott