The 290 has a wider field of view when compared to the 1120. Given the equal sensitivity of both cameras the wider field wins every time in my experience.
Now this 1/3 pixel thing bothers me. I'm not sure where it's coming from mathematically at all. This is from an Craig Stark's website (author of the original PHD)
"Without any noise, PHD is accurate down to (on average) 0.004 pixels or 1/250th of a pixel. With a low amount of noise, the accuracy goes to 0.018 pixels or 1/56th of a pixel and with high amounts of noise it goes to 0.18 pixels or 1/5.5th of a pixel. Better stars and/or better guide cameras will get you more accuracy, but even with this very noisy star, we're still at 1/5th of a pixel accuracy." ---
Long before you are going to get down to .1 pixels the mechanics of your mount and the seeing is going to be a problem. I can barely get 1/2 pixel accuracy when imaging a .7 arc seconds per pixel but I'm happy with it as that's .35 arc seconds. That's not going to ruin my images and it doesn't. On the other hand when I'm imaging with a guide camera a 2.28 pixels per arc second I can get down to this same accuracy which is near 1/8 of a pixel. So, that rule of thumb seems at odds with my own experiences recently.