No absolutely have never felt they are too high - I feel like lower would be annoying for conversation because when we host we routinely have people at the island while we are cooking and preparing , setting out food etc. I got our tiles from a local tile store- there wasn't a brand name on the box. it just said Made in Spain.

(A wall mount range hood is probably not what the OP asked for.) Mating to a 7.5 foot ceiling should not be difficult; even Wolf's large Pro Island hoods are only 18 inches high, leaving the base at 3 ft over the counter with a 7.5-foot ceiling. And higher helps the view across an island. However, unless the cooktop is only 24 inches, a 30-inch hood is too small for an island application. One needs to overlap the cooking zone on all four sides to account for rising plume expansion, and throw in a bit more size to account for cross drafts, depending on location. In any case, to say that the kitchen has a duct is far too little information. Where is the duct relative to the cooking zone, what diameter is it? Is there a blower at the other end or do you need one in the hood, etc? Can the duct be replaced?

I also appreciate walls, but prep sinks in islands are fine. It's the cleanup sink with its associated paraphernalia which Kitasei mentioned that are more problematic. That said, I'd sure rather have the dirty dishes on the island than the cooktop!! You know what's wrong with the cooktop there. Also, while it might feel like with pan frying you're spending a lot of time tending food, in general, at least for people who have a well balanced diet, well less than 20% of the cooking time is spent tending pots on the stove (there have been studies. I think the number is actually more like 10%, but I don't remember for sure). And when you are tending it, you're looking down. In other words, it might be a bit easier on the services location to leave them where they are, but you'll also have to put in a gigantor island hood if you want to prevent the removal of the wall to be a source of constant redecoration of your open space (i.e., more smells, grease, etc.). Walls, and locations away from the middle of the room, are great containers of the mess. They're also much safer because something unexpectedly slamming into a pot won't send it over the far side. Besides the whole splatter thing. We talk about keeping the stove in a "protected" area if possible, which also means guarding the cook from riffraff attacking her/his rear guard. That is, out of the most travelled spots. The open part where you're facing out into the company should be the least messy and dangerous, and what you'll get the most use of the openness out of. For most, that's the prep and baking areas. The low stink, fun, interactive kinds of work.

I may have left out some words due to repetition. The number of square feet refers to the entry aperture of the hood. For example, a 36 x 24 hood aperture would be 6 square feet, and would require 6 x 90 = 360 CFM actual, likely needing a blower rated at 540 CFM. Pressure loss not only entails the ducting, but the baffles and the MUA path. Leaky walls are not exactly a free path for air. A leaky house may be sufficient for MUA in practice (given that the blower rating takes the pressure loss into account), but the OP may live where aggressive code enforcement will demand at least a damper in a duct to the outside. The rationale for 90 ft/min is based on ensuring entrainment into baffle gaps that typically are around 50% of the baffle area and have to deal with upward plume velocities of as much as 1.2 m/s. See also the table (Figure 4) on page 9 of the Greenheck Guide available here: https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf The discussion leading to that table should prove useful for background information. In particular, the Greenheck method vs. the linear feet of hood edge (all the way around for an island hood) method is discussed. (Note commercial cooking rarely is true island type; even located in the middle of a kitchen the hood is connected to the cooktop via a back section. There may also be side skirts on the hood.) Last, let me point out that capture can fail under cross draft conditions, which are almost always worse for island/peninsula configurations than wall configurations.