chains always come too long, you measure to just fit the biggest gears (that you're not supposed to use together) and shorten the chain to one link more than that, then reassemble.

easily done with a chain punch.

9 speed chains are THINNER than 7/8 speeds, and 10 speeds are even thinner than that.

48:11 is a really tall gear. I find 48:13 is plenty tall for anything short of spinning down 35+ MPH hills

afaik, the 13-26 is the ONLY one I found with a 13 high gear in 8 speed, there's more choices in 12-xx.

here's some
http://www.amazon.com/Shimano-ICSHG5...=hg50+cassette

[those are really road ratios, not mountain, this cassette is part of both the Sora/Tiagra road gruppe and alivio mtn groups)

here's some more 8 speeds...
http://www.amazon.com/Shimano-HG-CAS...ef=pd_sbs_sg_4
http://www.amazon.com/Shimano-HG50-C...=hg50+cassette
http://www.amazon.com/SRAM-PG850-8-S...ef=pd_sbs_sg_3

(note each of those cover several different ratios)

warning, some HG50s are 9-speed, its downright confusing.