[2ndGoat]

I think people get a little caught up in characteristics of a given level at a given site. The games get tougher as you move up. It's just how it goes. Better players move up because they can, poor players can only lose so much money, and fewer people can afford to lose $10000 a year than can afford to lose $1000.

If you're a fantastic player, both 20/40 and 2/4 will seem like inviting fishing grounds. If you're mediocre the bigger game might look intimidating.

The differences as you move up come down to things like:
-fish may play more aggressively, even though they are still fish. However one that bluffs a little is significantly less profitable than one that NEVER bluffs
-you are more likely to see 5 half-decent players and 2 fish at your table rather than the other way around
-you will get checkraised more
-you will have to be more comfortable making reads in heads-up situations, where the correct decision doesn't smack you in the face quite as often as in a 5-way pot (in my opinion, anyway).
-You can usually count on one or two people at the table that play well enough that you just don't want to get in pots with them unless you have to

For the most part, planning ahead for higher limits can't have much of an effect on your end results- does it really make a difference whether someone tells you 15/30 is easy or tough? You'll find out quickly enough when you get there. If you're really interested, watch the tables for awhile.. sounds like you already have a little bit. That will probably be more useful to you than getting opinions from others' perceptions, where what we tell you may be tied more to the size of our egos than anything else.

2nd