A good graph with a properly placed transducer will work at any speed either boat you listed. My Elite Ti's work at 50mph which is as fast as my rigs goes. Still a bit confused about your efficiency questions though. You worried about only getting 3 mpg at cruising speed or 4. Or handling when the winds blowing 20 mph. Better yet, room for 3 people or just 2.

So you mention efficient a few times. So I put some numbers to it. Up to you what you feel is efficient. I picked a random lake and threw in some random numbers on navionics plotter.

Distance 4.2 miles I doubt you will be going further than that in between spot checking.

Speed 28 mph covers the distance in 8.59 min

Speed 36 mph covers the distance in 6.59 min

Actually three questions of which only the middle question has been answered.

#1 yes

#3 up to 15 mph

If anyone tells you that you can mark fish at 40 or 50 mph I would suggest investigating that before making a decision to buy a boat based on that input.

They will show on your graph at those speeds and with touch screens its easy to mark then circle back around.

Austin: it's a lot more efficient to let the fish lead you to the concentration of fish (just happened to be stripers in my video below) than it is to rocket all over the lake (although that is fun I will admit). If you really want to get into them, learn the technique below (and you can do this on any boat). Speed comes in if you want to get back in quickly (safety feature) or have a long run offshore or upriver - something like that. You'll want something that can go slow without fouling plugs for trolling and have room to get one aboard. Good luck catching them!

That was an excellent vid on high speed charting. Wish I could duplicate it - but 22 is all I do in the puddle-jumper.

There are a lot of things to consider before you look at speed...
1. How do you plan to fish? If you will be throwing artificials, you need big casting decks for the number of people you expect to fish with. Slabbing is not as critical but live bait you need the right sized round bait tanks or space for a bait tank.
2. How many people and types you plan to carry. I have kids so prefer high gunnels on a fish and ski vs big decks that my kids can fall off from
3. If you plan to cruise the lake scanning via down imaging then you will probably want to go around 30, if you are chasing topwater then binoculars and a fast boat
4. I go from spot to spot to look for fish vs covering the whole lake so I can go 35 between spots then use my thumper to call in fish or move to the next spot

I don’t run wide open between spots when looking for hybrids or striper. I rarely open my throttle over 2/3 unless running back to ramp to get home before wife gets mad!! As has been said layout and fish ability is more important.

Don't know if it's been mentioned, but if you fish on a boat long enough, you're gonna take that accidental look over your shoulder and realize that a storm is about to overtake you. In which case, you're going to want the fastest boat you can afford to get away from it.
Yes, you can mitigate that by watching the weather, phone alerts, etc. Just sayin. When the feces hit the oscillator, yer gonna wanna skiddadle.

Get the faster boat so few years later you don't have to say i wish...

No you aren't missing anything. Even when you have your transducer perfectly installed you'll be able to read depth (maybe) but actually you aren't going to be seeing schools of fish at 30mph and any structure you see will be questionable as far as accuracy. Striper fishing isn't a speed thing, it's a steady pace thing and putting in enough time to find the fish.

Got it! Thanks for so much information. Will opt for max hp when possible. Will set up another thread for another boat question.