I would say that in General, PRS Hollowbodies are more like the Gibson Semi-Hollow 335's than a PRS 'semi-hollow'. That maybe because the body of PRS is smaller, and therefore the 'hollow' space maybe similar to a large body 335 with a Centre Block. It may also be the difference between a Laminated and therefore consistently 'thin' top, back and sides vs Solid Wood that's 'carved' to shape. Not saying the Semi-Hollow doesn't make any difference, but I'd say its subtle at best - when comparing a PRS semi-hollow to the exact same model in a Solid version.
With PRS Semi-Hollows, the chamber can't be too big as the Mahogany has to be 'thick' enough to be the back and sides and the guitars aren't exactly that 'thick' to start. So I doubt there is too much 'flex' vs the semi-hollow Laminated wood style construction method used by Gibson.
The way I hear it - taking the fact that they are 'different' instruments made by different companies etc - PRS 'semi-hollows' are more like 'weight-relieved' Solid Body guitars than a 'traditional Gibson large body semi-hollow' and the 'closest' I can get is with a 'full' Hollowbody PRS. So if you want that more 'airy' 335 like tone, then go for the HB. If you want a lighter, incredibly versatile guitar - go for the Special.
I have the Special Semi-Hollow and both a HBii and 594 HB and 'both' the Hollowbodies have advantages to me over the 335 - the body size and playability, the modern features (Piezo or coil splits for example) etc and use these where I would use a 335 and the Special is more a lightweight (well 'light' compared to a lot of Electric guitars) versatile instrument.