Teleport could be out-ran by super speed without range IO's/SO's, but it had no maximum limit of "speed". In fact I'd say, an incarnate with cardiac would be better slotting a range IO in teleport than an End reduction IO, because a single SO of end reduction was the most you'd need and even then, end recovery mattered to for teleport efficiency. A person who recovers endurance fast enough wouldn't need any endurance reduction for teleport.
So without the root times for the teleport animations in front of me, just looking at City of Data's numbers shows teleport's cast time to be 2 seconds and its endurance cost to be 13. That means, given the residual hover lasts for four seconds, that teleport can be cast something between one port every 2 seconds and one port every 4 seconds, short of allowing yourself to fall. We can then estimate both the maximum straight-line teleport speed and its endurance burn rate.
Teleport's base range is 300 feet. 3-slotted to about the ED cap gets us to about 480 feet. Similar slotting for endred gets up to about 6.5 end. At those levels of slotting teleport's maximum speed and eps is about 240 fps (352mph) and its eps is about 3.25. 3.25 eps is not quite sustainable, but it can be sustained for very long periods of time if you have good recovery and start from full end. On a base 100 end character with the recovery of fully slotted stamina (about 2.5 eps) you have about 133 teleports of range, or about 63840 feet, or about 12 miles.
If we slow down our ports to about one every 3 seconds, we still don't fall down but we now have a sustainable teleport. Our eps drops to 2.17eps, and that's sustainable indefinitely. We now have infinite range and a speed of about 160 fps (about 235 mph).
If we don't slot for endurance at all, but we have maximal cardiac, we then have +45% endred. That reduces teleport's cost to about 8.97 end. If we teleport as slow as possible (once per four seconds) without falling, our eps burn rate becomes 2.24eps. That's also sustainable, at a teleport speed of about 120 fps (176 mph) with full range slotting. So that's possible, although you have to cut it very close on timing to be truly sustainable (say you're teleporting extreme distances in the Shadow Shard). In normal zones, even teleporting every 3 seconds gives a burn rate of 2.99 eps, which can be sustained for about 204 ports (18.5 miles).
The real problem with teleport range is turning off toggles and such. People often didn't like to do that. But if you have end burning powers on and you keep them on while teleporting for distance, its not uncommon to have net recovery in and around 1 eps, certainly less than 2 eps. That makes it very difficult to sustain a teleport chain. At 1eps net recovery instead of 2.5, the same Cardiac enhanced teleport at its slowest rate now only gets about 80 teleports before running out of endurance. Actually, its worse than that because you have to have the end to activate teleport. So really, once you drop below 8.97, you can't port anymore. That happens after about 73 ports. With range slotting that's about 6.6 miles. Good for short haul, pushing it for medium range, and insufficient to cross very large zones. And even if you make it, you're out of endurance when you get there.
Is it possible to run teleport with no endurance reduction of any kind, incarnate or slotting? Sort of. At its slowest teleport rate, an unenhanced teleport burns 3.25 eps. There are builds with more than 3.25 eps of net recovery, so its possible. But its not easy: base recovery is 100/60 = 1.67 eps. That build is running at +95% recovery (assuming zero end burn rate). And almost nothing recovers fast enough to run maximum speed teleport without endred of some kind. That's 6.5 eps, or +289% recovery (389% recovery total). You're talking about RA-levels of recovery to run that.
