funny. i was going to start a very similar thread today except i was looking at the r4 vs. hyperflex amp 6/4. the two price extremes of cold water suits. is patagonia really worth the extra cost? i know they make quality stuff and have a great warranty (though if they make really quality stuff, warranty shouldn't be an issue) but i could get 2 amps for the price of one patagonia and still have money left over. price is only an issue if i feel like i'm wasting $. seems like the wool lining in the r4 might be annoying, too.
I have an R4. It is very very warm. This past winter, I was sweating most days. It is not the most flexible suit. I don't really have anything to compare it to as it is the only 5 mil suit I've owned, but no flushing issues and no issues with the wool lining. The lining is a little weird at first, but definitely keeps you toasty.