It's difficult to compare displays of PB15 vs PB17 in general, I mean, make proper recommendations, since quality of the display might vary on these elder devices (reduced brighness / fading colors /greenish-taint).
I have both a 17"(normal-res) and a 15" DLSD (high-res) PB, but I cannot remember to notice any major difference of the displays except from their screen-resolution. I mean, not the kind of stunning difference like between the Powerbooks and the early-intel MacBookPros: the brightness and quality of the early-intels (A1260/1261) is simply blazing, compared to the PowerBooks.
About 17" high-res screens: my experience on my early-2008 intel MBP4,1(A1261) has taught me that it's BTO high-res display doesn't really matter to me. I've reduced screen-res from high (1920x1200) to normal (1680x1050), because my poor-vision does not cope with everything-too-small, when in high-res.
I guess, the 17" PB compares to the 15"PB in all respects but the screen-size and I think I personally wouldn't benefit from any high-res 17" screen, but would "downsize" screen-res to "normal".
Compared to the 17"PB the early-intel 17"MBP screens are so much brighter, which exceptionally matter's in daylight situations.