Hello Trish-

I drove from Ley Largo [Rick and Mary's] to Dallas last year in July. It took from 8:30am to 9:00PM the first day and from 4:00am to 11:00AM the next day. Thats taking the bottom route through Alexandria, LA. to Dallas. From Houston to Key Largo should be about 3-4 hours shorter. Don't ask what mph I averaged but think Texas Motor Speedway... Its divided highway all the way but the toll booths on "Main Street" in south Fla slow you down some but nothing like the road between Homestead and Key Largo. Areas to look for the law between Houston and Key Largo are east of Baton Rouge all the way to Mississippi, Florida panhandle to the big right turn south, all up and down the state of Florida. If you decide to take the western route passing by Tampa; the highway narrows to four lanes and the law stacks up there about six deep to just north of Tampa. I have driven this route from Dallas and Houston no less than six times in the last two years. I10 is NASCAR; so watch the rear as well as the front. Some students this time of year are going 90+mph in packs of four+ all the way to Panama City...

hope this helps,

thom