Lvling from 30 to 50 is really easy.. With a party you are able to gain 1000+ EXP for a chain.
I tried to lvl my r20 today and I got around 100 EXP for fighting one mob at same lvl.
As you remember the fights are much more difficult and take longer time now.
With that said, you are able to get EXTREMELY more EXP with a party and you need MUCH more time if you play solo. It's nearly impossible to play solo now.