Newer is not always better. IMHO test out for Yourself - this is no Firefox where You have a hard time to get different versions going
. I use the German RC as default already. If You ask me 1.5 with its new tabs is faster and even less resource hungry than 1.1.x. & I adore the XUL-made Preferences Panel...
You can install more than one version if You deselect multy user support ( = if You use as admin or know to set privileges, no multi user support means separate, independent profiles in each install directory) or create a profile with extra name instead of default before You install the next version. The first option is used chiefly by PPL that test - and or have a multi boot system. A k-meleon with Profiles in install directory can easily use the same Profile from different systems.
p.s. German RC. I was given to test. I even found an ancient typo - I had never noticed it in years (I never see any typos
).