"Quality" long runs

So I have been working on getting more running time in. For about the past 7 weeks I have slowly inched up my 2 long runs. One on Thursday and One on Sunday. The Thursday run I have come to realize is my quality workout; the one I feel most rested on and the one I am going to push the most, not intensity but distance. Last night I broke out the GPS Forerunner once again and set off knowing I would do at least 2 hours. I run around my neighborhood, lots of great bike trails to run on; I have several routes but decided the first route would take about an hour before circling back to the house to get a quick 30 second drink from the accelarade bottle. The second lap I take a different route but circle back a little quicker at about 50 minutes for another short drink, finishing up with a 2:19 run. This is my longest of the season and was 16.1 miles according to the GPS with 3,624 feet of climbing, not sure if the GPS is right on elevation, it does not seem very hilly, certainly no big steep hills, maybe just desceptively or gradually up and down more than I previously thought. My Sunday run I am usually still tired from the long Saturday ride usually 5 hours plus a short 30 minute brick run afterwards so that run has usually topped out at 2 hours to date. I will probably only push that one out to about 2:15 or so. My Thursday run I plan on getting to about 2:45 before my April Ironman race. That should be about 20 miles or so for me. I am struggling with knowing how far, how much volume etc but I guess everyone struggles with that part, so far I still recover weel between the quality workouts so that is key. The intensity is somewhat easy for now - keep everything easy and steady. Currently for me that is 145bpm or less on the hear rate monitor, to be honest my legs start to give out long before the lungs so this is usually not a problem for the longer stuff. I feel good about the long runs, in fact I have to say I look forward to the Thrusday night run every week. Last night the first hour and half was quite easy and I was jammin out to the new Rob Thomas tunes on the IPOD Delane downloaded for me. Even though I love to bike and I have started to like swimming much more than I used to, there is simply nothing like a good long run. Not sure what it is but I usually cannot wait to get started and just feel like I am crusing along effortlessly sometimes. Of course you are tired when it is over but you have the satisfaction of knowing you are doing all the things neccessary to get ready for Ironman.