Chart information: The vertical is typical Horsepower and horizontal is typical RPM range

In a regularly street driven application, the operating range of your engine will be from idle to some highway cruise RPM. For the sake of illustrating the difference of these two engines, the drivetrain is identical. The very first thing you should observe is that the OEM engine has a lower idle, and produces approximately 38 horsepower (the same as the Custom engine at 900/1000 RPM). OK, let's say you are sitting at a traffic light and you (normally) accelerate to 65 MPH to get on a highway, with your tranny in "D" or drive to let it shift "normally". The thing to notice here is that the used RPM range is somewhere between idle and 2500 RPM! Now notice the BLUE LINE and the RED LINE as you go up in RPM. The thing to consider while driving under "normal" conditions is; an OEM engine produces considerably MORE horsepower throughout the entire "normal" operating range! The Custom engine wakes up and starts developing horsepower around 3000 RPM then rapidly climbs the scale passing the OEM engine somewhere around 3600 RPM and continues to develop horsepower and peaks around 5000 RPM, where the OEM peaked around 4100 RPM. Another thing to notice is that the OEM engine continues to be the engine of choice all the way up to 4100 RPM, where the RED & BLUE lines cross. So in effect, the OEM engine is really the "high performance" all the way to 4100 RPM (peak horsepower).

There are some set ups that will give you the best of both engines. But these are generally expensive. Namely; Blowers or Nitrous.

You will notice that the blower & NOS rapidly climb the horsepower chart and goes off the chart at 3700 RPM @ 400 horsepower! This chart isn't scaled enough to get the full picture of a Blown or Nitrous fogged engine. However, you get the picture... if you want to have the best of both OEM and Custom High Performance engines, then a blower or Nitrous fogger is the way to go. On the other hand, if cruising is your thing,  and on a budget... then consider and OEM level engine as you won't be disappointed. The cool thing about blowers is they can be retro-fitted to an OEM engine without major internal changes, as long as it is done in moderation.  

NOTES:

A typical OEM engine would be similar to a stock 355 HP Chevy 350 SBC with a single four barrel 750 Holley double pumper on a dual plane intake.

A typical Custom engine would be similar to the Chevy 350 SBC equipped with Dart Aluminum heads, bored .030", forged pistons, hot roller cam, and a tunnel ram with a pair 600CFM Holleys.

There are countless combinations of engine set ups suitable for virtually any type of driving, cruising, and racing. The trick is to find the combination which best fulfiulls your requirements.

Case in point: Suppose you have a stock 350 200HP engine in your T Bucket. And you just got a hold of some "mad money" to burn. If you were to re-build your engine to make the "typical" custom performance engine you can easily expect to spend $2500.00 or more, if you build it properly. And, you will end up with an engine that won't cruise or drive as good as it did. However, It will run like a bat out of hell when you race it.

Now, take that same money and invest it in a 6/71 class blower and just hang it in your old engine. All of a sudden your low compression mild mannered engine is producing monster horsepower. You still get that good idle you like while sitting at a light, and you get G crushing accelleration as you mash the footfeed. Because it's a stock engine you do need you watch your boost. But 500+ horsepower isn't un common in a stock block assembly.

You can get similar results from nitrous (costing much less than a blower), but nitrous can be very rough on a stock assembly, especially pistons,.rings, and plugs. Also, to get full benefit from nitrous it is recommended to use direct injectors for the nitrous and fuel. This set up just sent you over the price of a good blower.

Moral of the story: If you crave the looks of a hot racing engine and intend to drive it, then consider a well built OEM engine and hang a blower on it someday.