Univega Gran Turismo, Guerciotti, Bridgestone MB2, Bike Friday New World Tourist, Serotta Ti
If you plan to use it in warmish weather then I wouldn't think twice about it. You'll see that there are thigh length pads out there. For comfort they are head and shoulders (and hips and buttocks) better than nothing. The full length pads are more comfortable.
I'm 6'3" and use a 6' pad. The 3" overhang doesn't bother me a bit.
Rivendell Quickbeam, Rivendell Rambouillet, Rivendell Atlantis, Circle A town bike, De Rosa Neo Primato, Cervelo RS
It depends on how much comfort you like. but I think it sound a bit short. Look a Big Agnes pads. They are not self inflating, and they are a bit heavier than the Prolite, but you can get long versions, they are far more comfortable and pack down to a smaller size.
I think it's a weight to comfort ratio problem. My first Thermarest was a full length, thick one. It was very comfortable, but it was also heavy. I had other items like that I brought on my first long tour - comfortable but a little heavy. It all added up. My rig weighed a ton and I ended up with a serious spoke-breaking problem the spoiled the second half of the tour.
Before my next tour a couple of years later I replaced some of my equipment - including my tent and my Thermarest - with smaller, lighter stuff. I still had some comfort items, but the whole rig was significantly lighter. I had a much easier time riding up hills, and didn't break a spoke.
The second Thermarest was a 3/4 length model. My torso and hips were supported, but my legs weren't. It didn't bother me that much and I felt the weight savings was definitely worth it.
HOWEVER, before my last tour I bought a Big Agnes Insulated Core air mattress. It's full length, more comfortable than either Thermarest ever was, much smaller when rolled up, and I think it's fairly equal to the smaller Thermarest in terms of weight. I love it! You have to blow it up every night, but it only takes me two minutes, and I don't mind. I also don't know how durable it will be. I'm worried because if it loses air it will be worthless, while the Thermarest at least has a little foam inside to cushion me if it fails. But so far, the Big Agnes has been a wonderful purchase.
In my experience the Prolite 4 insulates better and is less hassle than the Big Agnes people on here rave about. I use one of those compact Prolite 4s that only covers down to about my knees. I place some clothes under my feet as padding and insulation if its cold. I imagine both models are equally durable if cared for properly.