It's hard to say. I compared these exact two models at a store (for a friend). I couldn't properly compare them side by side because they were hooked up to a video splitter so I had the salesman connect them to the computer directly in turn (using an old ATI card, forget which one).
To my eyes, they looked almost identical to each other at 1024x768 resolution 85Hz. In fact, I give the edge to the EF70, which did look somewhat better/sharper, but this could be attributed to variance in manufacturing. To the best of my knowledge, they use the same Mitsubishi DiamondTron Flat Display screen. According to Viewsonic's web page, they both have the same misconvergence statistics. So based on my observations and the specs, the picture quality is similar.
So, I would have to say it comes down to whether or not you plan to use resolutions higher than 1024x768 (as the EF70 has an eye burning refresh rate of
66hz at 1280x1024, while the PF775 is
90hz). If you plan to (and want TCO 99, which the EF70 doesn't have), I think it would definitely be worth it to go for the PF775.
BTW, my friend ended up purchasing the EF70. Aside from some minor geometry problems (which seem to be common with these flat-display screens), it's a fine monitor with sharp text and bright colours.
Good luck.
Edit: Ok, re-read your post

If you're only considering picture quality, I would say it's not worth it at all, because IMO and based on the specs, the quality is practically the same.