IMO.....the bigger cubed motor will be at of an advantage due to the size factor. although getting a 350 to 1000hp isnt cost effective in my opinion. If you must use a small block, aftermarket big cube block all the way.So in essence it will be easier for a 434" small block to make 1000hp than a smaller bore to make the same power especially with the stroke difference in a 350 compared to a 400....bigger crank altogether. I am sure this could be fought over for days. if both motors were of equal hp/tq...identical cars etc....I think the one that would be the most reliable and consistant would be the bigger cubed motor just becuase of the heavier internals over the 350.