Which 2-stroke, 250+?

I'm very close to your situation, 57 yoa, knew I needed to get away from the 450 for the last several years.  Torn up lots of body parts over the last 40 something years of racing.  Offroad practice mostly now, A-rider, but probably closer to the average younger B rider pace now.  Occasionally still hit a local MX track. 18 XC450F has been my main ride for about 4 years.  A year ago I bought a almost new 18 XC-250, carb, kickstarter and E-start, one of the last light simple bikes.  On paper, it's the perfect bike for me.  Almost every track I go to though, I feel better on the 450F.  Fast, rocky, jumps, sand, flowing woods= I end up preferring the 450, mostly due to a wide spread of power. But, I've had a couple whiskey throttle moments in the last few years that cost me.  99% of the time it's no problem, but it's scary when it is.  Now, when it gets really nasty and/or slow, like 10 mph and under slow, the 250 2 stroke shines with an almost unstallable motor and a front end that feels so light you don't feel "stuck" in a line or ruts.  The weight of the 450 seems to go away once you get over 10-15mph.  But for the last few years, I don't go if its going to be a mud fest.  I also discovered I just don't trust the 2 stroke on bigger jumps, but I think that has more to do with riding 4 strokes 99% of the time in the last 2 decades.  Anyway, I really planned on turning the XC 250 into my main race bike, but I gave in and have a new 23 Gasgas EX350F sitting in my garage right now.  Can't comment yet, as it just has one heat cycle on it so far, but I think I will love it.  With the rebates right now, I think they get the easy nod over the YZ-250 (I've owned and raced many, including a awesome 93 YZ-360 Noleen).  I bought a skid plate, seat, bark busters, fan, hour meter, and a bag of goodies, so I'm not sure what the OTD price was on just the bike, but it was under $9k!   Now I need to decide if I get rid of my 18 450 (90 something hours) or the 250 (only 26 hours I think).  It's actually a hard decision, but I know the 450 should go.      

I'd personally go for the 250SX. Maybe wait a year of 2 though to sort out the FI and electronic power valve.

That sounds like a awfully good deal to me.  For us older mostly off-road guys, I think the older/softer feeling frame (4-5 pounds lighter) is better. Next years GasGas will probably follow the KTM and Husky and get the new frame and the spring forks.  I'll get rocks thrown at me for this, but I actually like the light AER forks and the ability to run them low psi for tight/rocks, or pump them up if I actually go to MX and/or faster sand tracks.  I'm also not a fan of the TPI, which is why I specifically got a carb bike.  But, I'd probably take a TBI over either.  Sounds like it would be a great bike for you, especially at that price.  Honestly, I've seen used bikes selling for more than that.

I wasn't seeing a 250 MX bike as being easier to ride than a 450. Great choice.