Thanks for the input, which was very helpful in weighing a big financial decision. Based on being a new boater with desire for family reliability and what I've read about the 2002 Mercury 115-HP ELPTO 2+2 motor, I have decided to re-power.
The shop I referenced is an authorized dealer for Mercury, Suzuki, Honda, and Tohatsu. I don't know how much the owner makes off of selling each brand. His opinion is that Mercury and Suzuki are now both making very reliable motors. He generally recommends Mercury Pro-XS with the Command Thrust option for performance applications at 115hp. Since Suzuki (and all manufacturers it seems) share design and components across similarly sized engines, he conducted an experiment where he "tuned" a 115A to match the 140A factory specs (ECU, etc) but saw minimal increase in real-world performance on a matched boat (hull, mounting set-up, prop, load, conditions). He also ran the Suzuki 115A vs the Mercury Pro-XS 115 CT and saw significant performance gains with the Merc which is why he uses this configuration on his bass boat. I don't think he is as familiar with performance characteristics of Suzuki 115/140 B generation engines, though he thought they would have similar performance to the A generation. I include his recommendations here for others benefit as "real-world" comparisons are rare. However, his experience may not be directly applicable to Suzuki's B generation of 115/150hp motors, if their performance characteristics are truly improved.
For benefit of future users considering similar repower applications, I have attempted to summarize manufacturer specs comparing the Suzuki DF115B/G or DF140B/G with Mercury Pro-XS 115 or 150 w/ Command Thrust motors:
Suzuki DF115/140BG: Info at
https://www.globalsuzuki.com/marine/lin ... mation.pdf.
Weight for B model is 410 lbs with "drive-by-wire" or "Suzuki Precision Control" adding ~4.5 lbs for BG model. Design is DOHC, 16 valves, inline 4 with 2.045 L displacement. Full throttle RPM range is 5700-6300. It does look like the Suzuki B generation was "re-engineered" with gains in compression ratio (now 10.6, up from 9.7) as well as durability improvements (water detection system, cowl air/water intake separation, larger fuel filter, larger fuel pump), direct ignition, and tweaks to simplify oil change. They also have self-adjusting timing chains. These motors weigh a difference of 2 kg (4.4 lb), with the 140B lighter than the 115B (per the spec sheet). With regard to performance characteristics, the B generation appears to have slightly better fuel efficiency, slightly higher top-speed (1.3 mph). Both A and B generations have an "offset drive shaft", which depending on the significance of this design could theoretically help w/ stern "heavy" properties of 16 and 18 foot early 2000s Ventura/Dauntless models. Likewise, the gear ratio of 2.59:1 allows use of a large pitch, large diameter propeller.
Mercury Pro-XS 115 w/ Command Thrust: Info at
https://www.mercurymarine.com/en/us/eng ... 115-150hp/.
Weight is 360 lbs, or maybe slightly more w/ larger Command Thrust drive unit. Design is SOHC, 8 valves, inline 4 with 2.1L displacement. Full throttle RPM range is 5300-6300. Mechanical throttle control. Compression ratio not listed. Command thrust gear ratio 2.38 by using lower unit from 150hp engine which also allows larger pitch/diameter prop selection. Not as much information regarding internal motor design which can be objectively factored into durability, reliability, maintenance, etc.
Mercury Pro-XS 150 weighs 456 lbs for comparison and is by many accounts one of Mercury's best outboards but perhaps too heavy and "overpowered" for my application. Including here for other's future reference. For folks repowering Ventura or Dauntless 18/180s, they will likely be looking at Merc 150 (456 lbs) vs Suzuki 140 (410 lbs) in which the Suzuki has the ~50 lb weight advantage.
Given the immense knowledge/judgment/experience of others on this forum, I'm hoping someone might be able to help predict how these engine characteristics and features would translate to real-world ownership and performance differences on 16/18 foot Ventura/Dauntless models.
It seems like the Suzuki 140B has advantages over Merc Pro-XS 115 CT for both advertised horsepower and gear ratio (2.59 vs 2.38). Conversely, it weighs 50 lbs more.
Q4: On this a 16-foot hull, would [a SUZUKI DF140B] result in noticeable performance differences in torque and power for improved acceleration and time to plane under load with total boat weight of 3000 lbs?
I boat on freshwater lakes.
Q5: Would having a higher powered motor on what's known as a stern-heavy boat affect resale value?
Venturas are a bit of a unicorn, but many Dauntless 16 boat are available, so more power may make boat more attractive to buyers.
Q6: Is there any advantage to having "drive-by-wire" on a hull of this vintage for recreational lake fishing and skiing?
My inclination would be to keep things simple and go with mechanical throttle control if that means less risk of problems in the future.
Q7: When repowering, are what other systems are worth upgrading or replacing for a 20 year old hull?
Thanks again to the community--you are a major reason why I bought a used Boston Whaler boat.