6 units should be the maximum and I'm basing this on no testing at all.
271 is the standard starting jump speed, which when divided by tickrate (66.666) gives 4.065. And because we know* they require the psuedo ground, 6.065 should be the max.
To get up to a 7 unit teleport (assuming everything else I've said so far is correct) you'd need a jump speed of 333.333+ or a tickrate of about 54, neither of which are easy. Gravity also shouldn't affect anything because we only care about the very first tick and gravity shouldn't be important in that situation.
I'm also choosing to ignore that you can do a regular jump without crouching and get 276.013275 u/s because it only gains .0751991 units over a regular jump.
*I'm assuming there's no other stupid engine bug we don't know about yet
If you time a rocket to hit on the same tick you uncrouch and jump, you can reach 790+ u/s.
I tested this but that doesn't seem to work, I assume its because you can't jump when you take damage, so if you manage to time the rocket to hit at the same time, you can't jump.
What I did is I made a tas recording of an uncrouch bounce on 1081 units, wich is also a jbug height. Then I raised the tele to 8 units in hammer, recompiled, reloaded the tas and made a checkpoint right after the tas fires the rocket.
So I know the rocket was gonna hit the ground at the same time as me. (As Im writing this I realise this might be wrong since you uncrouch in the air to reach the ground and skip a few units of falling, so the rocket wouldn't hit the ground at the same time as you in this scenario)
Anyway, I would then reload the checkpoint and retry the jbug over and over. When I believe I was hitting hit, I would still get tele but my character would jump after tele, wich I assume is because I hit the jbug but got hit by the tele on my way up from the jump so I was telehoping.
Like I mentionned, my rocket timing might have been off, and Im not sure how you could set it up perfectly to be able to test efficiently. You might just need to manually time the rocket and trials and error until you either win or telehop.
Edit: I tested again by just trials and error, and I got a few telehops without hitmarker but also a few WITH a hitmarker. So I don't think its possible, again probably because of jumping while getting damage.