. . . My iC706 can't zerobeat very well and I want that function. . . .
Let's see if we can save you some money --
. . . What procedure do you use to "zero-beat" on the IC-706?
I've forgotten if there's a dedicated "CW zero-beat tone" generator on that rig. But what works on _every_ modern rig (including IC-706, which I used heavily for several years) is:
. . . turn BK-IN off (so the rig doesn't transmit when you press the key)
. . . hold down the key (or paddle) so you get a side-tone;
. . . tune the rig until the sidetone pitch matches the pitch of the signal you want to respond to;
. . . turn BK-IN on (so the rig transmits when you press the key).
You will be "zero-beat" (within a few Hz) with the incoming signal. The process only takes a few seconds, even if you have to change the "tuning speed" during it.
I _suspect_ there's a way to generate a "zero-beat" signal using one of the front-panel buttons, but I haven't checked the manual.
Now, if you _can't hear_ the difference between two different pitches, that would be a problem. But it's a rare condition, and you'll have the same problem on the IC-718.
The IC-718 doesn't have much better performance (if it's better at all) than the IC-706. I don't think you need a new rig to solve the problem.
On filters, I had an Icom 350 Hz "CW/RTTY" filter on my IC-706, and it was "just right". The W4RT filters might be better, though.