Here is another method to help with determining your training pace for various types of running workouts. Your VDOT!
VDOT paces provide quite similar results as McMillan Running Calculator but only provide one specific pace for a particular type of workout (Easy, Threshold, Interval, etc) versus a range.
VDOT was created by famous American running coach Jack Daniels. Without getting into the details, VDOT is a simple way to define your current running fitness. By cross referencing a recent race time (5k-marathon) using the VDOT tables, you can determine your current VDOT fitness which is defined by a number (30-85). The higher the VDOT number, the greater your fitness. This VDOT number can then be cross-referenced with a second table which provides your training paces for Easy, Marathon, Threshold, Interval, and Repetition workouts. Pretty sweet!
If you are looking for a bit of training guidance this is definitely a nice crosscheck.
What do I like about the VDOT paces? They are based off of your current fitness level. I feel this will help reduce the change of injury and burnout. Training like a 3:00 marathoner when you are in 4:00 shape seems like a pretty slippery slope.
When can you increase the training paces? If you feel like you are more fit, prove it in a race. If the race result confirms a higher VDOT value, go for it. One thing to note though, Jack does recommend training at a particular VDOT value for at least three weeks before moving to a higher one. After the third week, you could then start training at the new training paces if you so desired.
If you don’t have an opportunity to race during your training cycle, Jack recommends that you can increase your VDOT by one after four to six weeks of training at a particular VDOT assuming you feel like the workouts are getting easier.
You can check out Daniels Running Formula for the tables, training plans, and training guidance. Runbayou also created a very nice VDOT calculator that combines all of these tables into one easy to use interface. The calculator is slick and definitely worth a look!
I am currently using the VDOT approach and even though it is fairly new to me, I feel it has already helped with preventing over-training as I increase my weekly mileage. I like it!