Caching is all about performance, so I carefully track Dalli performance to ensure no regressions.
You can optionally use kgio to give Dalli a 10-20% performance boost: gem install kgio.
Note I've added some benchmarks over time to Dalli that the other libraries don't necessarily have.
Testing 1.8.5 with ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-darwin11.2.0]
user system total real
set:plain:memcache-client 1.860000 0.310000 2.170000 ( 2.188030)
set:ruby:memcache-client 1.830000 0.290000 2.120000 ( 2.130212)
get:plain:memcache-client 1.830000 0.340000 2.170000 ( 2.176156)
get:ruby:memcache-client 1.900000 0.330000 2.230000 ( 2.235045)
multiget:ruby:memcache-client 0.860000 0.120000 0.980000 ( 0.987348)
missing:ruby:memcache-client 1.630000 0.320000 1.950000 ( 1.954867)
mixed:ruby:memcache-client 3.690000 0.670000 4.360000 ( 4.364469)
Testing with Rails 3.2.1 Using kgio socket IO Testing 2.0.0 with ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-darwin11.3.0]
user system total real
mixed:rails:dalli 1.580000 0.570000 2.150000 ( 3.008839)
set:plain:dalli 0.730000 0.300000 1.030000 ( 1.567098)
setq:plain:dalli 0.520000 0.120000 0.640000 ( 0.634402)
set:ruby:dalli 0.800000 0.300000 1.100000 ( 1.640348)
get:plain:dalli 0.840000 0.330000 1.170000 ( 1.668425)
get:ruby:dalli 0.850000 0.330000 1.180000 ( 1.665716)
multiget:ruby:dalli 0.700000 0.260000 0.960000 ( 0.965423)
missing:ruby:dalli 0.720000 0.320000 1.040000 ( 1.511720)
mixed:ruby:dalli 1.660000 0.640000 2.300000 ( 3.320743)
mixedq:ruby:dalli 1.630000 0.510000 2.140000 ( 2.629734)
incr:ruby:dalli 0.270000 0.100000 0.370000 ( 0.547618)