Hmmmm... The receiver and amp upgrades in question were 7 to 8 years ago now, so I hate trying to grade them. Also, they aren't ideal comparisons to your case. (The Yamaha receiver was a Pro Logic unit replaced by an Outlaw 1050 that had DD/DTS decoding and a better-than-average amp section.) Having said that, the Paradigm speakers that I added because of the receiver upgrade audibly benefited from the addition of a separate amp - most notably at medium to higher volumes.

As for the 7125 and 7200, I haven't heard either - I've used Outlaw's original 750, the Model 200 monoblock, and the 7500. Based on what I know of them, though, the real difference between the two is power. There are some large rooms and some very inefficient speakers out there that can need the extra power. There are also folks who just want the "peace of mind" of extra power. The two amps are built by the same manufacturer in California with comparable components.