You're talking about a 15 year old design, there.
I drove a GTA 1000 from 94 to just last year. I too, loved it.
I have used the 250 for just about an hour, on barren ground, so cannot speak for it's performance from personal experience.
I use a Teknetics Delta currently, and can say with certainty that it beats the snot out of my old GTA.
BTW: The GTA beat the snot out of my AT4 that I used from 1988 to 1994. The AT4 beat up my Freedom ACE, which beat up my previous BFO unit.
The technology keeps getting better, but the real x-factor here is the detectorist, and his command of his machine.
There are people here still making wonderful finds with all the detectors mentioned in this post.
Some, even won't consider a modern unit when the break or wear out their current detector.
(Leslie, I am speaking about you

)
I for one would trade out the GTA for a 250, 350, or AT Pro. But that's just me. (I still have the ACE and AT4 )
I traded even the GTA for the Delta. I am now detecting to buy the AT Pro. (I'll keep the Delta)
Haven't actually used any of my own money for a detector since 1984. I trade for a new one, or use found money.
Whatever you decide will work. Remember, it's the driver that makes the most difference.