Impedance matching with tube amp


Hi there,
The title might be a bit misleading or even plain wrong...

I have a pair of Wharfedale Diamonds 230 powered by a push-pull tube amp (15w TR / 25w UL - more than enough for my listening space/habits) with 4 and 8 ohm taps. The speakers are 8 ohms rated, but the minimum impedance is quite low... 3.7 ohms. Unfortunately I haven't been able to find the impedance graph online, but the min. impedance info of 3.7 is quite revealing. If in any way similar to other such speakers, I'd expect the impedance dip to be around 200-500Hz range, more or less. In any case, the speakers go low, there's no way around that.
Now, I can connect them to either the 8 or 4 ohm taps, but I'd like to know which way is the best both in terms of protecting the amp/tubes/transformers and also which way would yield better SQ.
From what I can tell, reading different stuff around the net:
  • 8 ohms tap: theoretical impedance match, should be "safer" (?), but will the impedance dip put more strain on the amp?
  • 4 ohms tap: could probably better deal with the impedance dips by delivering more current, danger of running higher voltages/temps though?

Maybe I got some things wrong and you can hopefully correct me. But at this time, it's not clear to me which way is the "better" one.

So, I realize this choice really depends from case to case, but with my speakers which tap would be more preferred?
Would the 4 ohm tap deliver more power into the speakers where/when they require it, so it will better drive the speakers?
Is it in any way dangerous to use the 4 ohm tap, since I understand it needs to push more voltage into the tubes? Maybe even shorten the tubes life? Or is it the other way around?
I feel like I got some misconceptions around this particular subject. Right now, the amp and tubes are brand new and the short tests I did on both taps did not reveal any significant differences to me. If anything, I feel that the 4ohm tap has tighter bass (more driver control?) but the 8ohm tap sounds "fuller"... But I don't know if that's just the placebo and being biased by everything I've read so far...

Thanks for helping!

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