You mentioned trail. I would surely stay away from the big bikes. If you are a moderate rider, start with a small bike and as you get better, then move on to the big bikes. I haven't riden with you, so I don't know what type of rider you are.
How about a dirt bike that is dual sported? Everyone has "their" brand that they lean too. If it hasn't been said before. "The rider makes the bike, not the other way around."
If you are doing any type of moderate trail riding. The BMW650 and KTM 640...(690 is the new one coming out) will be too big. Just think picking up those heavy bikes when they fall over. The gnarlier the trail and the heavier the bike, the quicker you will wear out.
If you aren't doing any serious road riding. How about a big bore dirt bike? Honda XR650, Husaberg 650, KTM 525/530? The Honda would be the better one for any of the onroad duties. All mentioned will go over 100mph. I have seen the XR650 on single track...it can be done...
This is how I pick what bike I will own. What do most of my buddies ride? Chances are someone will have parts in the tool box. Is it a popular bike, alot of dealer support? For long trips, can I get parts on the road. Yes, Triumphs are cool, not many dealers out there, on the other hand, there are a slew Honda, KTM, BMW, etc...dealers out there.
Remember: Four wheels moves the body, two wheels moves the soul.
Back to back The KTM640 and the BMW f650, the KTM wins because of better parts hung from it. I am not saying that because I own a KTM. You have to throw more money at the already expensive BMW. To get it near the KTM's performance. The dollar goes farther with the KTM. Both will get the job done, it comes down how much you want to spend, and how the job is handled.
More road: heavier street oriented machine
More dirt: lighter dirt oriented machine