I have 5.4.11. If your computer use SSE2 you should shooce this variant. When you have unzipped it and run the installation process you the will have
this: 2006-10-14 02:04:28||Starting BOINC client version 5.5.0 for windows_intelx86
2006-10-14 02:04:28||libcurl/7.15.3 OpenSSL/0.9.8a zlib/1.2.3

Your Boinc-version is still 5.4.11 yet.
If you not have 5.11.4 you can open a project and download this Client from there.