I will also add, £250 Russian agency girl is mid range plain looking
Looks are always subjective - there are £600 girls on Diva I wouldn't touch with a stick but my taste is by no means the gold standard here.
The real problem with £600 is rather that I highly doubt that the level of service becomes twice as good. I understand the WG will look more attractive but the potential for a bad punt is still there (despite great reviews here). For the same amount you could go for someone like Cathy Heaven who has proven exceptional DT skills (if she happens to be in London) OR do a longer booking with a trusted SP (or try a duo booking). You could also justify it if the WG provides something that's rare to find but based on a cursory search of reviews here these pricings tend to be a trap for people who don't mind throwing their money out.
Just look at this review to see what I mean -
https://www.ukpunting.com/index.php?topic=310472.msg3247116#msg3247116 These type of reviews aren't unusual here.
I have had no issues paying the £250 but in my review I also mention alternatives that I think offer better relative value at that price point. At the end of the day it's for people to decide what they prefer but I don't think it hurts to be a bit more conscious about these things.