I've owned both the EC250 (2002) and EC300 (2006 current bike). I loved my 250 but unfortunately it got stolen... After nearly switching to the dark side (4 stroke) I decided to replace it with the 300 and couldn't be happier. if you're coming off a 250f you should
really consider the 300 as it produces very smooth yet strong 4 stroke type power without the added weight or maintenance costs. Oh, yeah and the 300's plenty fast too (an even match for any YZ450F or CRF450).
I find the 300 easier to ride than the 250 over the course of a day as well (less tiring)
Plus I've found the GG's to be ultra reliable (my 250 had over 5000kms on it when it got stolen and I never had to do anything other than normal maintenance...)