I would say the Statements have a little bit more impact than the ER18. Both the Statements and the ER18 play pleasingly low in the bass arena, IIRC the ER18's F3 goes down into the high 20s (not sure about the Statements). That said, I've never listened to my ER18 and been disappointed in the bass, but when they were side by side I think the Statements had a tiny bit more "kick".
Regarding the clarity... again they both have great clarity. But, I think the edges are a bit sharper in the midrange department on the ER18 (again, just my opinion). They both have great highs, you can almost look into the music while it's playing but the ER18 is a bit sharper IMO.
I use my ER18 for a strictly music system. I use an older Adcom GFA-5500 amp, a B&K preamp and a Marantz SACD player. The amp is rated at 200w/ch at 8 ohms and 350w/ch at 4 ohms, if anything that's conservative. I know the Statements like power, and actually what I've found is that for both the ER18 and the Statements you gain a lot of clarity and bass with better power. I tried using a Harman Kardon HK-3490 (rated at 120w/ch) to replace a vintage Pioneer SX-950 (rated at 85w/ch) that I was originally using and I was thoroughly disgusted with my decision; the Pioneer mopped the floor with HK in terms of sound quality and power. Needless to say I returned the Harman Kardon and that's when I decided to get Adcom amp and the preamp. Finally I had a remote, plus I got away from the bugs associated with vintage receivers, and still have great sound. Not sure how much you know about the vintage audio, but it takes a lot of "modern power" to match the headroom in one of those older, silver faced receivers. As an aside, I still LOVE vintage receivers; I picked up another Pioneer SX-950 that I use in my shop.
Regarding how loud they'll play... My dad has made the Statements "pop" once from going too loud, but he powers them with a Pioneer SX-1250, which is a monster of a stereo receiver in terms of power output, and he was really hammering on them pretty hard (pretty sure he also had the bass knob turned up about 3/4 too). I've never made the ER18 pop and I'm definitely not nice to them (I don't boost bass or treble at all, everything is flat). Anyone that's had listening sessions with me knows that as much as I love clarity, they also need to survive the volume knob if they want to live in my house
. The ER18s do that very well IMO
I chose the ER18 over the Statements because of their size, the ER18 is a LOT smaller than the Statements. If aesthetics didn't matter and I had to make a blindfolded decision as to which speaker I liked better, I honestly don't know which I'd choose; they're both an incredible pair of speakers. I might lean more towards the Statements just because I love bass, but I don't know. Like I said, I've never been disappointed in the bass output of the ER18.