Sounds like overclocking the Nexus is not realistic option, considering you can't bump the CPU too far. The Quadrant benchmarks show that the Galaxy Nexus's dual core CPU blows away my OC'ed single-core Thunderbolt @ 1.8ghz.
Again, the 2gb RAM on the U.S. dual-core S3 is very tempting though...but probably not worth the extra $200. Ugh!!
Do the speakerphone mod apps work on a rooted stock-rom Galaxy Nexus? If so, can you recommend the best one so I can tell my friend? Again, his speakerphone audio was barely audible, even in a quiet room.
I see that you are right. 4.2 is out for non-Verizon phones, but it looks like you can custom flash a Verizon phone to 4.2, albeit it seems a little buggy. At least that's more progress than the s3!!!