I liked what I saw on the KDE live Mint
I advise you to partition your HD using one of the other distros. Or use the GNOME Mint LiveCD, and stop the installation process after the partitioning is done. Then boot the KDE Mint LiveDVD to install into that new partition.
I too had a multi-boot setup, until an (attempted) installation of KDE Mint damaged the boot. Its partition utility is not to be trusted, IMO.
Do back up your important files before trying the install!