It's a mistake that many folks make to think that driving slow is easier on an engine. It all depends on what load is on the engine. The conditions of highest Brake Mean Effective Pressure in the cylinders are at low RPM and high throttle setting. If you lug your engine, you are creating the condition that will help identify any possible weakness in the head gasket or weakness in the bearings.
We've had an 87 wagon that went 235,000 until I hit a deer and had to replace it. The 90 Legacy Wagon replacement had 267,000 on it when we sold it to buy a 2002 Forester.We take a 2000 mile trip twice a year for work purposes. We stick with manual because I like the better control on slick surfaces. I shift up around 4500 and down at around 2500 to 3000 depending on load. I use 80 mph on the gage when the signs say 70, figuring that spedometer error will take care of the diff. So far so good on the ticket situation.
Although I rev the car fairly high, I seldom floorboard the throttle. I raced sports cars for 8 years with only one blown engine. "Babying" an engine can do more harm than good.
Dick