Hi Scott,
I was only using the 128mb as an example. These 99 folders, with the 20 styles/songs per folder is available on any size sd card. Your only restriction is the size of your styles and the capacity of your card.
ie sd cards are available at the moment ranging from 8mb to 256mb. You certainly won't fit 2000 styles on an 8mb card, wheras if you bought a 256mb card for only saving styles, it might be overkill as you could have wasted space left on your card.

I mainly use my 256mb card for sd audio files for my kn7.

I personally decided I wanted to have seperate cards for individual functions ,
ie
I have my old gm midifiles and songs dowloaded from the members on 1 card.

I have all my styles on another card that I use for auditioning when I'm looking for a style to go with a new song.

Last, I have my work card. This contains the styles & songs & setups for the songs that I can actually play.This ones really empty, but I'm hoping to add to it Heehee.

I worked out what size card I'd need if I was planning to use it to it's full capacity( 99 folders by 20 styles/songs) by working out roughly how many styles/songs I'd get to the 1mb and multiplying.

The sd card is very quick for loading
( about 3 seconds on my kn7 for a style).
But I can really only comment on my kn7 as I haven't seen the kn2600.