Woodrow nailed it. Here is the thing (and I'm the same size as you) as big as you are and the power your used too, you will not have any fun on the 125 especially if your in the woods or doing any kind of climbing. You can be fast on a 125, but it takes years of riding one to do so. I've owned them all. The 250F will have the torque for you to have fun on and you will love the usable power it has. As far as reliability, the fours are more reliable until they get wore out then they are expensive and timeconsuming to work on (alot more moving parts in one). You can do a topend on the 125 in about an hour, but will take about four times that on a thumper. But it all boils down to money. If you going to keep them of course you will want to mod them a little, It costs ALOT more to mod a 4 stroke than a 2. A great bike for trails and beating on is the KDX 200. Most reliable 2 stroke ever made with the perfect amount of power, and they made them for years so you can get them cheap!!!
As far as the 500 zingers guys, There is a reason they stopped mass producing them and it wasn't cause people weren't buying them. You can only go so fast on them though because you can't get them to hook up or keep the front wheel on the ground. The 450F is actually a rideable bike with power you can use. You can be faster on the 450F unless you have balls the size of a car.