More rpms = more HP and less torque, thats why F1 cars make like 800hp on a 3.0L v8 which also makes about 200tq, they rev to 24,000 rpms. A 351 will rev about 6k or so assuming you have the stock bottom end.
MY 351 See's 7k all day long on the track, stock crank, rods, forged pistons, clevite bearings balanced to .5 grams, and it has yet to have a problem in the last 3 years.
the car leaves at 3k at the track and run s 6.4x's all day long on the laughing gas
You will more power with a 347 than with a 351 with the same HCI. But you will have more bottom end torque at a lower rpm with a 351 than a 347 (just my opinion). It is all about the bottom end at that point (compression ratio, bearing clearances, etc) with the same HCI. 351 has more rotational mass and larger bearings (read: more bearing surface means more frictional losses but stronger overall), which will affect power ratings. A 351 does have a more favorable rod to stroke ratio, a little stronger block, and the ability to stroke it out to 408 c.i. It is hard to compare the two because you wouldn't put the same cam or probably even heads on a 347 and a 351. It is all in the complete setup. That is only my 2 cents, though.