An all-out 5K will definitely give you answers. When I had this concern a few weeks ago, I was concerned that I was running easy/long runs quite a bit faster than McMillan said I should even though they felt easy. I was using my 5K PR from 3/3. But that was my first race effort since injury so I probably left a little time on the course because I was worried about reinjury, and it was a hilly course. Ran all out on a flat 5K on 4/6 and set a huge new PR. Plugged those paces into McMillan and the numbers it spit out for my easy runs are more consistient with what I've been hitting. So May 11 should be a great indicator.

 

Good.  McMillan isn't the end all and be all but it is a pretty good guide.  If you're running a good bit faster than McMillan suggests, then you either didn't race all out or you really are running your easy runs too fast.  Another good guide is found here.  It's based off Daniels and it doesn't give a range of paces; it gives one pace.  It tends to have faster paces for faster work but a slower easy pace.

Tonight I finally ran a sub 9 min/mile 10k tempo, it wasn't easy I will be honest. While my stupid Garmin Communicator Plug in is still trying to install, I will just state a few things.

  I started  out just above 10 min/mile pace, I hit 3.1 miles in 28:08 minutes and took a breather. I then hit 5 miles in 45:16 minutes, took a moment to breath as a side stitch was trying to attack me. 

  My plan was to run a 7 mile tempo, but I decided near the end to run a 10k tempo and then a 1 mile cool down jog then a .3 mile walk.

  Overall I ran 6.2 miles in 55:14 with an average pace of 8:55 min/mile, my fastest PR before this was 58:55 with an average pace of 9:29 min/mile so I kicked 3 minutes off. Honestly I probably wouldn't have if I hadn't stopped twice for a minute break to breath and get over a side stitch. Anyways, my splits were:

Mile 1 - 10:08

Mile 2 - 9:00

Mile 3 - 8:20

Mile 4 - 8:49

Mile 5 - 8:58

Mile 6 - 8:26

.2      - 7:51

   Then I tried to jog an easy 1 miler afterwards to cool down, I ran that in 9:30 so it was relatively slower and felt easier than the tempo run (go figure). Then I walked the remaining .3 miles back to my Tahoe and now I am dealing with trying to get my stupid Garmin to pair and connect and transfer to the computer so this is very irritating!

    I wasn't going to do a tempo this week, I wanted to focus on what seems like a new found pace and speed, but I decided after mile 1 to just go for it and experiment and boy am I glad I did. Not only is this my fastest 10k yet, my goal this year was to break under the 9 min/mile barrier for a 10k and I did that tonight. Now that I have checked off......... I wonder when I'll be able to break the 8 min/mile barrier for a 5k (hmm....).

  Can somebody please help me with this damn Garmin before I throw it across the room 

I like my tempo run to be just 2-3 miles shorter than my long runs, maybe it's not a tempo run but I call it that. My easy runs are 5 miles (sometimes 6) and my long runs are returning back to between 9-11 miles (still recovering somewhat from my HM almost 3 weeks ago). Technically I'm probably only doing a tempo 3-4 miles out of that 6-7 mile run. I try to use the first 2 miles to warm up, then either the last mile to slow back down. And I took advice from someone on here who said that a tempo should be about 70% of the long run (I think that is what they said)... other than that I can happily say that doing my tempo this way for the past 5-6 months has helped me, my HM almost 3 weeks ago is proof of that, so I am going to keep my tempo runs 6-7 miles, my easy runs 4-6 miles and my longs run no shorter than 9 miles with the hopes of hitting 12 mile long runs this Fall. I like my training, it has shown great improvement, and I will keep it. 

Eh, I don't explain things very well, it makes a lot more sense in my head......... but I don't know if any sane person would want to go there 

My "tempo" runs might be more like progression runs I think, but I'll call them tempos cause RA and RW don't have progression runs.... though I could create them. I use those runs to play with my speed, work on maintaining a hard effort, medium effort, and sometimes strenuous effort for 4-5 miles... for now. Sometimes if I am feeling real good, I'll try this on my long runs around 10-11 miles, just to gauge my fitness and condition.

Anyone can check out my training plan for this year, at the end of the year I am going to assess my body, and improvement and if all is good and great, I'll up my long runs between 12-14 miles for the first part of 2014, tempo/progression runs between 8-10 miles, easy/recovery runs between 5-6 miles and maybe add an extra day who knows. If this year goes without injury and comes with great success at my 3 Fall HMs, I hope to increase 2014 weekly mileage to between 30-35 miles.

I have become very flexible though, and willing to change anything if need be. 

You've been running for 19 years? I didn't think you were that old

This is from a rw article from back awhile ago. I have no idea if the statement about Pfitzinger and 9 mile tempo runs is accurate as it is not a direct quote from Pfitzinger.

"Maintaining a specific and consistent pace is the most important aspect of a tempo run. However, this doesn’t exclude variety in other respects, depending on a runner’s individual goals. Says Pfitzinger, "The tempo runs I use for my athletes most frequently are four to six miles at 15K to half-marathon race pace." For marathoners, Pfitzinger prescribes up to nine miles at between half-marathon and marathon race pace, or a 13-mile run followed by five miles at between half-marathon and marathon pace."

http://m.runnersworld.com/workouts/what-exactly-tempo-run?page=single

I am 33, started running at age 14.