Hi all, based on its length the I-Max is close enough to be regarded as a .64wl NOT a 6/8wl as I previously stated, the I-Max 2000 will have a small dbd gain advantage over a true 5/8wl antenna, but not so much that the human eye or ear could discern the difference.
Grounding ANY vertical is desireable, mainly to reduce static which can be a real pain at times. It is good practise to use large diameter ground wire, and keep it as short as possible, running it to a COMMON connection in the shack, to which all RF equipment should be connected. You should be careful that the length of ground wire is NOT RESONANT at the frequency of operation, otherwise it will be ineffective, and may contribute to RF entering the shack. Also, keeping the antenna as far away from the shack as possible is a good idea, otherwise RF may enter in even with good grounding. Sometimes it may prove necessary to use ferrite rings or clip-ons to cool a hot mic. It's wise to use a LOW PASS FILTER such as the Kenwood LF-30A, and in addition, the use of a LINE ISOLATER (or two) such as Radio Works model T4 Plus, both exiting the rig and at the base of the antenna. This helps eliminate RF returning into the shack via the coax shield. It is wise to watch the VSWR when using Line Isolators as high levels can cause them to run kinda hot, but, at CB output levels it might not be a problem!
OK all, I hope all this is of some help to you, I'll be offline for some time, so don't expect a come back to respond to any aspect of this anyway soon.
Good luck and 73.