What project are you using now?
As for 150" UST, you sort of can with the MKII or PX3-pro. Caveats are that you need a light controlled room and not care about 3D. One of the guys calibrating the MKIIs has been playing with calibration for 150" screens and is saying that he has it going.
To be honest though, I wouldn't recommend going UST at this point for that big of a screen unless you either didn't have room for a long throw (my issue) or you have a older, lower end long throw and need to upgrade but don't want to hit JVC prices. The USTs have a much better price point.
I don't want to hit JVC prices, because I will likely never do that unless I win the lottery. I'm a cheap bastard and always doing a cost-benefit analysis on most large purchases I buy.
My room is completely light controlled, which is a plus, and I also don't care about 3D.
My throw distance is super fixed and I have it maxed out at what current (not UST) protectors can do for 150". (around 14')
I currently have an Epson 4040 that doesn't even support HDR; so I am looking for an upgrade. I'm not excited about shelling out 5k for that upgrade however.
I'm currently split at about 50% gaming, 50% TV/Movies at the moment, so low input lag is important to me. I'm seemingly stuck in no-man's-land at the moment.