There is no real difference to fly these two.
The DR380 is just the largest 180 bhp engine version of the 300 series, which came out in the late 60's and were replaced by the 400 series in the early 70's.
What you do not say is whether you have been flying the DR400/108/125/160 or 180 ?
They all fly the same but with more power with the larger numbers.
The DR300 series had opening doors and the DR400 series had a slide foward canopy which is better for wind noise and visability.
some of the latter DR400's had disc brakes but many older ones have been retrofitted.
All of them are great tourers except the small engine ones.