My understanding of soft proofing is that it allows your software to show what the image would look like on different types of paper. It's a function in Lightroom (for sure - don't know about other software). It's mainly used to ensure you get the levels (brightness and contrast) right for that paper type. 9/10 times I use it, it's like someone moved the contrast slider half an inch to the left. Google will be your friend for more [less biased] info.
My experience of it is that it's a bit of a gimmick. There's nothing that compares to holding the print in your actual hand and looking at it in actual normal light without a backlit monitor.
If I'm ever unsure of which paper to print an image on, I print it on both. Over time, that allowed me to make the judgements I made above. Ultimately, it's about what you want to infer with your print. When I looked at it, it was a technically accomplished image with nice colour tones, sharp, defined edges, and quite high in contrast. If I were to print it, I'd go gloss. Specifically, Ilford Gold Fibre Gloss.
