You have to decide what you consider a “modern” engine. Fuel injection? Overhead cams? EGR? By and large, modern engines make more power than older (even pre emission) engines. I have a 95 Range Rover with a 4.2L V8. Pushrod, EFI, distributor, no catalytic converters or OBD II equipment. It made 200 hp. Wife has an 08 Range Rover with a 4.2L V8 (mild factory supercharger) that makes 400 hp.
IMO, a six speed transmission is ideal for almost all vehicles. Fewer is limiting, more is constantly gear hunting or changing 5 times from 0-30 mph. My favorite engines have all been slightly oversquare (stroke about 75% of the bore), large displacement per cylinder, with both low end torque and heads that allow higher RPM airflow. What you end up with is something that can be lugged and short shifted, (or just not shifted) as well as something that that can be revved out and driven fast and hard.
To pass someone you can simply add throttle, you don’t have to drop multiple gears to get the revs up, and then change up several times while passing to keep it in the powerband.
When it comes to automatics, the only ones that do what I want them to are made by ZF and Allison.
Something like a 6.0L V8 that makes power from 2,000-8,000 RPM mated to a 6 speed ZF would be bad medicine.