I agree with boddyfodder that you can choose a non 100Hz mode on the DX150. It's called DRC-50 and still employs some digital wizardry to double both the horizontal and vertical resolution but is 50Hz. The What Video website seemed to prefer that to the 100Hz modes, but as often gets posted on these forums, the reviews should be taken with a pinch of salt. There's no 50Hz option on the FQ70 though.
Another difference between the two sets is the Scart options. The FQ70 has two RGB scarts but the DX150 only one. This is possibly beacuse Sony thought you would be using the digital tuner instead of an external Sky digibox.
I personally bought the FQ70 and I am very pleased with it. I haven't bothered to tune in the terrestrial channels yet so I'm mostly enjoying RGB digibox pictures. It does seem to handle terrestrial pictures from the VCR comfortably though. The weaker Five signal gives a touch of flicker although I will notice defects compared to the superb digital picture.
My FQ70 does suffer with a bit of upward red bleed, which seems to be a characteristic of this set. On most pictures it isn't noticeable but red on white shows it up - e.g. Sky Sports News or the BBC One logo on a white background.
Thanks to this thread, I might have a tinker, writing everything down before changing anything

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Sony FQ70 small problem
The two red settings (cut-off and another) are both set much higher than the blue and green - this could explain the bleed but may mean washed-out reds if reduced.
Both sets could be bought for about £900 - Currys are even doing the FQ70 for £845 delivered but only until today and online.
James