With your high HP goals, I'd stick with the stock 3.58" stroke. Going with a 4.05" stroke and that much HP puts too much strain on the thrust sides. At a 1000 HP, unfilled blocks have had a tendancy to crack the cylinder walls. Looks like the cracks usually start at the bottom of the cylinder on the thrust side and works its way towards the top. Some of the cracks that I've seen haven't gone completely to the top of the cylinder, stopping short about a 1/2" down. I have a partial filled block here that'll get about 1300 horses thrown at it. I guess we'll see soon enough is filling the block is enough.

Edit: These were 4.05" and 4.08" stroked 6.1 blocks. Also the 5.7 has a stronger main web design than the 6.1.