One has to examine their riding speed and longevity aspirations a bit more than you've described. Unfortunately, I don't remember where I read about it (It may have been the Thorn Forums in the UK and their focus tends to be on rugged expedition gear, but I do recall one users experience with the the SP PD-8x. He was happy with the Dyno but disappointed with the longevity and the company made it clear these are not designed to be rebuilt.
One always gets what they pay for, but all too often that last little bit of performance, durability and design smarts come at a steep cost. What sort of riding do you plan to do? On road only or off road? I would consider that because of the speeds reached on good smooth roads tend to be high enough that worrying too much about the Nth degree of efficiency may not be worth extra cost but if you go slow, like I like to, or off road, you may want to look at a more efficient hub.
The absolute most efficient and rugged, designed for year of use and insane mileage is the Schmidt Son 28. I have one and have had two others over the years. Where the Son 28 makes a difference is low rolling resistance (though I've never really been able to tell while riding compared to my less efficient Shimano hubs) and they are reputed to be the very best in charging efficiently at low speeds. They are I believe at full charging capability at 15 kilometers per hour vs 19 for the smaller lighter Son Delux.
I'm not sure how that compares to my Shimano. I tend to not fret over small differences in performance but charging at slow speed is imprtant to me, since I go slowly and always charge my cache battery, which is in line to the GPS and acts as a buffer so I don't worry about constant shutdowns on the GPS or the iPhone. I like to be able to run the lights at the same time. I do quite a bit of riding at night. Your needs might be quite different.
What I sort of learned the hard way however is that sometimes little details make a huge difference in use over time. I've found the hookups to the Shimano, which is the same as on the Precision shutter dyno to be a pain. In the first place I've already broken one. In the second it's not as elegant to put in clips for two wires and the more breaks in the wire the more likely the problems. Thirdly they are a bit more fiddly to take on an off for wheel swaps or flats repairs and the plastic clips are far less robust compared to the spade connectors. Since I have several wheels, some light, some heavy - I like to be able to interchange wheels but the different connecting systems make that impossible. I regret not sticking to one over another style. If I had to start all over again though, I'm not sure which would win out, quality and a small performance gain, or economy.
The one thing I can say for sure however is that I'll never ever build a wheel without a dyno. It's just so nice to have. Good luck.
Oh, one last point. I save a heck of a lot of money by ordering dymos and light from overseas. The shipping hurts but not if one waits and buys several items at once. My next purchase will be to upgrade my Bush & Mueller CYO lights for a couple or Schmidt Edelux II. My lights are fine but the Edelux has such a nice broad even illumination, somewhat more even and wider than mine are, is metal compared to plastic and even the switch feels better to use. Life's short. Spend foolishly.
