Instant - sounds like you are pretty much at the same sort of level that I am, except you have more experience with foils, having the 16.5 Warrior.
It sounds like you have already decided to go for the Psycho, but are just contemplating which size. Oviously it will depend on what sort of wind range you are looking for, but I presume you want it for when you need to pack up the 16.5 Warrior, i.e. 30kmh and above, about 16 - 17 knots and up.
All I can tell you is from my own experience so far. Just so you know, I am not yet the official FS dealer for Israel, although this is my goal, within the next few months.
175lb is about 85kg right? Which makes you about 10kg heavier than me. I have used the 12.5 Psycho only, up till now, from 10 / 11 knots, up to 22 knots. At 22 knots I did not need to use the de-power trimmer yet - you will definately not need to. I recon I will handle the kite without trimmer a little above this wind speed, and up to about 30 knots with trimmer, once I get more experienced with it.
Do a search for all of my posts regarding the Psycho, I have given my observations from the very first day riding with it, up till now (about 3 weekends worth). I have tried to remain as objective as possible, but it is definately a great kite. It takes a bit of getting used to (probably less for you having foil experience), has an awsome de-power range, impressive speed, and very nice jumping ability. I am still learning it myself, but I am sure once I have it fully wired, that I will be jumping as high, or higher than I would on tubes, with definately longer hang time - this I am feeling already.
You say the dealer is your friend. Well then surely he will let you have a few test runs before you actually have to lay out the dough