I'd prefer somewhat higher frequency though, more in line with thier X series, but without major increase in TDP. But I guess +10W is tolerable for a good processing power increase.
I'd be hesitant to judge those AMD processors on the specified clock, even more than usual.
The usual argument is that clocks are not comparable, because you don't know that a 4GHz cpu A is not slower than a 1GHz cpu B in doing a specific task. That I assume is known around here, but is not what I mean. AMD is marketing the feature of those processors to overclock automatically above the specified turbo clock. Meaning 3.9GHz should be a lower bound, and it is completely possible those cpus will routinely clock much higher in practice. See http://www.kitguru.net/components/cpu/jon-martindale/amds-ex... (and it is also as XFR in the original article here).
Or maybe they won't overclock well at all. Well, we'll see after they were released.
Edit: I just realized that with regards to the specific comparison I answered to my point is moot, because according to the table in the article, the Ryzen 7 1700 does not have that feature. The Ryzen 7 1700X does. That might make picking the right processors more difficult than usual. I'll let the comment stand regardless, that feature and distinction might not be well known yet.
If you do any substantial overclock, meaning you are going to do a little bit of over voltage, the presence or lack of XFR matters little, and you are definitely going to go above turbo core freqs. XFR is going to be a nice-to-have unconditionally because of it being on the fly adjustments, but it does not seem to be a feature that it is going to make you buy an X version over non-X. It seems to me it will come down to the classic spend less risk more, spend more risk less in terms of overclock, just like it was for vishera 8320/8350/9370/9590 , so I don't expect many features differences between the versions.
I guess it matters for single core performance bottlenecks. I.e. let's say you are compiling. Higher frequency CPU will manage it in less time. More cores naturally help as well.
Comparing to my current Haswell CPU, that's quite a great value for the money:
(84W TDP, 4 cores, 8 threads, $300+ price soon after launch, 3.4-3.9GHz).
I'd prefer somewhat higher frequency though, more in line with thier X series, but without major increase in TDP. But I guess +10W is tolerable for a good processing power increase.