I have not heard the SFM 160's, but have a close friend who runs Power 3's with big Dunlavy SC-V's and I have spent many hours listening to his system. As for the amps drifting in and out of bias, he has never reported that problem. In fact, he has had no problems whatsoever with the amps, despite driving the hell out of them (his system can go LOUD and does so often) seven days a week. He has had them for a year and a half without so much as blowing a tube. Returning to the issue of power, the Power 3's each put out a solid 220 tube watts backed by a serious power supply and, I am confident, will outshout by a large margin virtually any 250 watt solid-state amp. Again, as for the SFM 160's, no clue.
As for the cost of the Power 3's, because their sound (and thus, reputation) is controversial, they can easily be had used for less than $5,000 (if you are posting threads, I would imagine you know this) and are sometimes advertised for as low as $3,500. The knock on the amp is that it is too "solid-state" sounding. I personally disagree with this, finding them to have the "rightness", for lack of a better term, that characterizes the tube sound, but it is true that they are not bloomy in the midrange to the degree that many tube amps are. Most people report that the amp is significantly better sounding (and more punchy and bloomy, i.e., more tube-like) if run with Svetlana KT-88 powers tubes instead of the stock 6550 tubes. Presumably in response to this perception (perpetrated by Stereophile), Sonic Frontiers re-released the amp in "Special Edition" version with the Svetlana KT-88's and other enhancements. The Svetlana's cost the same as 6550's, I believe (but only the Svetlana and VAC's KT-88's are reliable, so be careful in buying). I have not heard the amps with the Svetlana's, by the way. To conclude as to the "solid-state sound" issue, it would not hurt to pair the Power 3's with a slightly "bloomy" tube pre-amp, like the VAC preamps (which are wonderful, by the way, even the Standard model). My friend uses a CAT Mark III pre-amp with his Power 3's with great success.
In any event, my subjective impressions are that they are great amps. They are VERY solidly built and come with a sturdy tube cage that is easy to take on and off. They have a stand-by mode which allows you to leave them for hours and then return, with no warm-up wait. The only downside is that, like the other large amps, they take up a lot of room, especially because there are two of them (my friend has his in the basement, under his speakers).