I feel that if you have an automatic, you can do wonders with the 383. The manual car might be better suited for a high revving 350. . . but I would still choose 383 over 350 any day of the week.
My 383 feels much more powerful than my former 350. Winding things at a higher RPM could spell trouble for your entire drivetrain and bottom end, including the pump in your automatic transmission, torque converter, your ignition system (Opti sucks after 6500rpm), and other items spinning on your car.
The fastest Lt1s tend to be a 383, or 396 with over 500hp and torque at the crank. To get that kinda of power from a 350 requires a barely streetable cam and other goodies. Look at the AI website. . . the world's fastest NA LT1.....is a 383.
For the 383, I think the increased power comes from not only the longer stroke, but the fact that a 383 breathes deeper. Therefore a 383 with a healthy cam and heads, will walk all over a high revving 350. I've seen it time and time again. I think a compromise woudl be an LT1 377. I've seen a guy get 525 RWHP and 480 torque pds from one with a smallish cam!
If you go 383, use the right components and you"ll NEVER go with a 350 when you have the opportunity.
Anyone else wanna chime in.