2nd hand Kia Rio or Kia Ceed

Hello, I'm new to this forum, so hoping for a bit of advice. I've recently started a new job where I am doing a lot of motorway miles. I expect to be doing 15-20K per year. We already have a family car, so I'm ultimately looking for something that is nippy on the motorway with long drives comfortable but doesn't cost a lot (original budget was £5k all in but looks like I might have to stretch to £5.5K). I also was looking for 5 doors with enough room in the back to put 2 kids in when necessary.

Having test driven a few cars, I've pretty much set my heart on either the Kia Rio or Kia Ceed. I've seen 2 that are possibilities, but not sure which is the best choice.

Rio 1.5 Diesel: 11 reg, 36,600 on the clock £5357 (told by dealership that they don't negotiate)
Ceed, 1.6 Diesel: 09 reg, 60,000 on the clock £5499 (though dealer said he'd do a deal if we call back and say we want it)

With the Rio dealer, there were a few other models that were older but slightly coming in under £5k also diesel:

Rio, 09 reg, 49,942 on the clock
Ceed, 08 reg 45,711 on the clock
Rio, 09 reg 33,366 on the clock

I liked the feel of Ceed, as it had an executive feel to it, i think I'd be comfortable on the ride, but I'm concerned about the age/mileage of it and whether it would last, so the Rio would be the alternative. I'd love to hear from people who know about these cars and whether they would still hold up with the mileage?

Thanks