I think the only way to know is to get a sample and try it on site. Paint can look very different depending on the quality of light you have.

Well a complication is the white subway tile we're going to put in the kitchen seems to match Heron Plume. I'm not sure if we want to match it exactly or go a slightly darker shade for the walls, but the good thing about Heron Plume is that although it is "warm," it is less warm than the Modest White. (My eyes are very good at seeing slight variations in color.) My understanding is that with dark wood cabinets (like dark walnut) you want to go warm with the white paint. Definitely a cool warm would clash with them, except maybe Eider White which SW lists in their cool whites but definitely tends warm. Another issue is that there is a small white armoire and the window/door trim is painted a bright, reflective white, which might be another reason to go with a darker white for more contrast.

Somebody posted a picture of Modest White darkened by 50% and it looks about as yucky as the color I'm planning to cover up! Good example of the difference between a paint chip and painting an entire wall.

I'm going with Eider White. Some people complain that it "pulls pink" - but that's exactly what I want. All the articles on choosing a white say to use warm whites (i.e. pull red or yellow) with dark cabinets. SW lists it as a cool white and my eyes can see the slightest bit of purple (not pink) in the sample chip - but it's only a tiny fraction of difference from the closest warm whites like Heron Plume, Incredible White, Toque White. In the SW Whites brochure, Eider White looks warm compared to the other "cool" whites they include.

Don't underestimate the value of painting a large sample (like a foamboard) and viewing it in your space at different times of day and in different parts of the space. Also be aware that the color of the "horrid orange-beige" walls could alter your perception of the color you are testing. Depending on how dark the orange-beige is, you might want to prime before testing colors. Or at least leave a white border on your test foam board so that you aren't seeing the white up against the current color, which can affect perception.

I ordered a large paint sample sheet. Based on what I've read, an actual paint sample of Eider White will not show the actual color because the gallon uses the smallest measure of mauve (?), so a smaller container will be pinker than the actual color. I'll probably get a whole gallon, paint swatches around the room, and if it looks horrid I'll cover it with something else.