What dirt bike?

Ok, I'm a while away from getting dirty, but keeping my eye open just in case a bargain happens my way.
Question is, what to look for? I rode MX for years before I went road, so don't want anything I will grow out of too quickly. I've ridden every MX 2T from 80cc to 500cc and enjoy a good dose of power.
However, I'm looking at trail riding so want something I can rec register. Not keen on the big 4t MX horror stories, but are the same reliability issues on things like the xr600?
Is lower grunt but lower weight going to be easier to flick through the scrub.
I guess I'd look at 250-300cc 2t or 400-600 4t??
So what's good, what's to avoid & would it be worth finding a full on 2t MX KX250 or similar that has been converted for rego?
Question is, what to look for? I rode MX for years before I went road, so don't want anything I will grow out of too quickly. I've ridden every MX 2T from 80cc to 500cc and enjoy a good dose of power.
However, I'm looking at trail riding so want something I can rec register. Not keen on the big 4t MX horror stories, but are the same reliability issues on things like the xr600?
Is lower grunt but lower weight going to be easier to flick through the scrub.
I guess I'd look at 250-300cc 2t or 400-600 4t??
So what's good, what's to avoid & would it be worth finding a full on 2t MX KX250 or similar that has been converted for rego?