when you put n02 in the equation these things change.
sure a 434 will run much better than a 355 without n02. but when you plan to use no2 then it is easy to surpass the safe limits for a stock block even with a 350.
Furthermore, NO2 also build torque. In fact, it typically builds more torque than hp.
Here is a nice 350 with NO2 article. 500hp and 584 ftlbs with a little 100 shot. I bet a 200 shot would get it to 600hp and 700ftlbs.
so, building a 434 will allow you to run less n02 than a 350 to reach the same power level.