Pass XA30.5 vs. X150.5

What Jtinn said.

Is the power output between the X150.5 and the XA30.5 very different?

Yes, 150 watts versus 30, but the XA.5 seem to be conservatively rated, at least they sound that way. You should be ok with the lower power with speakers 89db or higher, less then that you are probably pushing it.

My speakers are 92 db and 4 Ohms, but they have lots of drivers 2-10", 2-7", 2-3" and a tweeter (Montana XP, plus I have a large room (35 x 25 x 10 foot ceiling). I was just wondering if the additional price of the XA30.5 used was mainly because of it being a newer model, or is it also better in performance?

Completely different animal, XA.5 is Class A and the the X150.5 is A/B - 99% of people will tell you the XA.5 is the far better amps in the Pass product line. I think you would have no problem with the XA30.5 power, especially with a 40hm load. Call Pass or Reno HiFi, they will give it to you straight as to whether the match is suitable.