Machining cost

You'll probably want to figure out the least amount of overbore it will require to keep the block as thick as you can between the cylinders. If it only needs .030 to clean it up I would go .030. Parts availability is another one to look at. See what pistons and rings and all that are available in a different bore size, ie, more choices out there most of the time for .030 or .060 than .070. Your block will pretty much tell you what total cubic inch you will end up with. My 383 was bored .060 so now its just shy of 396 cubes.