We've had both. A 1999 Ford V10 with the 4 speed and a 2005 Chevy V8 with the 5 speed. The Chevy is clearly the more powerful engine and with the 5 speed, it makes a significant difference. The difference is primarily on grades. On a long pull, the old Ford would struggle at 25 to 30 mph when pulling our 4,600 lb Jeep. The Chevy would pull the same grade at 35+ mph. Both engines would be roaring but at the end of the day, both made it to the summit.
We sold the old Ford with 101,000 miles on the clock. In 3 years we added 30,000 miles and never had a problem. Started immediately and just kept on going. We've only had the Chevy for 2 years and have only added 9,000 to the clock. So far, it has performed very well.
Our Ford was the early, I believe 2 valve engine and so far as I know never had the noted spark plug issue. The Chevy had an after market program that bumped HP and Torque so 275 HP on the Ford and 400 on the Chevy. Both would do 75+ on the open road with no problem. The mileage on the Ford was better, maybe .5 to 1 mpg.
As said, go with the floorpan that works. Both engines will get the job done.