I would go for the the Rega R3's at that price. (They were a £500 speaker up until the RS3's were launched.)
Not just because they are my own speakers - and I like them - but because they are 89db efficiency (6 ohms) and the Dali Lektor 2 are 85db (6 ohms).
With a 25 watt valve amp you are going to need that extra 4db efficiency/sensitivity.
Not only that, but they are not fussy about positioning (with respect to distance from the wall) and - being floorstanders - you are not going to have to spend out on a pair of good stands like you would for the Dali's.
(And bearing in mind your partner, I think the R3's look much nicer than a pair of Lektors, especially if you consider how ugly most speaker stands are and factor that in too!)
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