So I got into a huge argument about KTM EXC's vs. the FSE for nothing.
OK, I think you're somewhat crazy, as I am sold on a 4T for Dual Sport use, but you have a plan and want some input. Regarding the big bike little bike theory, my friend has a 200XC and a 300DE. He convinced his wife to let him keep the 200, he was going to ride it in the tight stuff. Now it sits most of the time, he has been corrupted by the 300's nice power. The difference in handling nimbleness in the tight stuff to him is negated by the torque of the 300.
Can you ride other peoples bikes? That is the best way to solidify what you like and don't like.
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"Conviction is a luxury of those on the sidelines."
'13 Beta 300RR - race bike
'02 GG300XC - "Billie Baroo"
'01 DR650
'02 GG 280 Pro
'06 YZ 250
'07 WR450
'00 TT125RL
'94 YZ200 - custom keeper