From what I've read and my own personal experience, it's usually best to wait until 3 years of age before breeding Pituophis. Some people "power feed" their colubrids to get them up to breeding size quickly but Pituophis have very large eggs and seem to do better when raised on a more typical feeding schedule (once every 7 days or so). I would think that a less than optimum sized pine would be at greater risk for becoming egg bound too.
Some pits can be prone to going into a chronic regurgitation cycle when they are fed very large prey items. This seems to be more common in some of the more slender pits (i.e. vertebralis, jani, affinis, etc.) but can probably occur in any of them. If this ever happens with your pines, don't offer them anything for atleast two weeks and then start them on very small prey items.
If your black pine is easily getting the rat pinks down and they're not leaving an obvious bulge than you'll probably be fine moving to the next larger size.
You don't have to be too worried about it but when in doubt, go with the size you know they can handle.
Here's a couple of my hatchlings from last year...
<img src=http://gila.fieldherpers.com/Photos/bp1.jpg>
<img src=http://gila.fieldherpers.com/Photos/bp2.jpg>