You must not ride hills or weigh more than #170 then!
My 350 is too slow...
I ride hills (mountains, to be exact) and I'm well above #170 and my 250 pulls me up anything no problem. *shrug*
The ONLY place my 250 would be 'too slow' would be a fast fire road or open desert. No way no how is it ever 'too slow' in single track.
On a similar note, did anyone catch the GNCC round where Kailub Russel (current champ on KTM 350) rode a 150 XC and was leading all the 450s until he had to pit with a stick in his rear brake or something? The only place the 450s were faster were the wide open grass sections, and it still wasn't enough. So yeah rider/skill > bike/displacement every time.