Zach, a good start is that within your point blank range (PBR), you generally don't have to take angle into account. Just so we're on the same page, by PBR I mean using typically between a 200 and 300 yard zero (depending on the chambering and your comfort level), and holding dead on to a little past that on game, often 250 to 350. (I do shoot farther than this, but use turrets or dots for correction) Since what angle primarily does is reduce the distance that gravity has to work on the bullet - effectively shortening the range, if the true range falls within the PBR so will the effective range (barring very high angles and a maxed out PBR).
Beyond that, the greater the range and greater the angle, the more quickly it matters.
Here is a drop chart for my 7/08 AI, I used
JBM's free software. Drop is in inches (normally I use MOA, but inches makes much more sense in this discussion). The colored numbers are the CHANGE in inches for the angled shot vs a flatline shot, at the given range. I decided that under 1.5 inches change I would consider noise, so the numbers in red are for situations I'd ignore the angle, and the numbers in blue are for where I'd try and factor it in.
Using the logic above, it does actually turn blue at 150 yards at an angle of 45, but since I have a modest sight in distance, I'm still only 3.1" from point of aim, which I'm comfortable with for big game. For most practical purposes, angle EXTENDS the distance at which a dead on hold is appropriate.