I own the YZ450F and it has PLENTY of power. I recently rode a WR250F, 03, and that bike was a blast. Very nimble, comfortable and the power very usable and controllable. The suspension was quite nice in the woods. I didn't get the bike on the track but I feel it would handle it with to problem. Riding the WR on the track would require adjustments to the suspension but that is easily accomplished. Plus, the WR can have the timing modified to the YZ timing and you will have a screamer of a trail bike.
The YZ will have a stiffer suspension, less flywheel weight, and will rev quicker than a WR. This will make it "feel" more powerful that the WR but it is merely a "seat of the pants" feel. If you are going to trail ride 90% of the time, go with a WR. If you are going to run on the track 15% of the time or more often then get the YZ.
For comparison, the WR has a larger tank and E-start. The 03's have auto-decompression so there is no "drill" in starting them. You'll be happy with either of these bikes.