I'm getting close to replacing my 140/80-15 rear tire.  My plan is to put the 140/90 on, and, since my ride is 70 miles/day in a straight line, I'm looking for a long-wear cruise tire to meet the need.  Any suggestions?

I second that.

Hard compund/high mileage tires are not as safe.  That is the trade off and since you are a high mileage rider you'll increase your risk level by using them.  Much better to buy a really good brand of tire instead, because they've already engineered a good compromise in mileage and traction.

I changed my IRC rear tire at about 6000, and now my Dunlop is still going strong after 7000 more.