Like all intervals, these are a good training exercise, but I think they are very ineffective at predicting the full marathon time. It's a good workout because you're working on the basic principles of intervals - a structured period of effort and rest.
When I was running intervals I would usually do 8 repeats off a shorter rest, maybe 1:40, and would consistently record times of 3:15-3:20. Given that the exercise plans equal rest (eg 3:15-3:20 for me) I'd comfortably expect to do the whole 10 repeats at that pace. But I've never had a lot of long runs behind me and my 2 marathons are both very close to 4:00. The thought of doing a marathon in 3:20 is way beyond me. This makes sense to me too - the marathon is 52 times the 800m distance, yet this calculation only multiplies the time by 60, despite the obvious differences running such a long way will make.
Race predictor programmes and tables also have a role, but your best bet is to train, run a few races, and try to improve. You know whether you ran well, I wouldn't place much faith in these type of calculations.
You can see my training log if you're really bored: [url]www.veganfitness.net/viewtopic.php?f=8&t=16086&start=360[/url]