jonnyy40 - If you compare 15" and 17" screens side by side the difference is huge. As marky says, a 17" TFT is the equivalent of a 19" CRT, so if you're happy with a 19" CRT then you'll be happy with a 17" TFT.
I run 2 x NEC 1760NX TFT's which the last time I looked were £395 from Technoworld, which at the time were offering the best deal on these. Definition is outstanding - and very much better than both the Hansol 710P and the Mitsubishi Diamond Pro CRT's that they replaced. No flicker, sharp text right up to the edge of the screen, no reflections, and a bright vibrant image. And best of all, no eyestrain!
I've put the 17" Hansol CRT alongside as a 3rd screen, and the difference is stark! Configuration with a Matrox G550 was easy and self explanatory.