For me, the 150s simply offer more SPH (smiles per hour). I bought my 150 as a play bike and wound up selling my 450 bc i always rode 150 whether for MX or XC. I periodically ride other people's 125s and it makes me appreciate the 150 even more. It allows me to be a bit sloppier than the 125s. This is due to the added low-mid torque the 150 offers over any 125 I've ever been on.
It sounds like you are moving away from racing exclusively. This is where the 150 shines.
I randomly bought a 250SX a while back, and honestly, when I go riding, no matter if MX or off-road...im never sure which one I'm taking until it's time to load up. I can assure you, if I had a 125, I would leave it at home anytime I was going off-road or play riding.
That said folks who ride/race MX exclusively tend to prefer the 125 due to its longer over-rev pull and don't mind losing the increased low-mid torque the 150 offers.
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