Tests begin on Canaries telescope
The GCT is a clone of the Keck and uses the same 36 hexagon mirrors with essentially no gaps between them to give a mirror approx 10m diameter, it is fractionally larger than the keck for allegedly engineering reasons to do with a different mirror polisher but probably to claim the largest title!
Having said that the 4x8m mirrors of the VLT can be combined to be larger.
Salt and Hobberly-Eberly don't really count in the same way - they are made up of spherical mirror segments and cannot form a (high quality) image - both are used as light buckets for spectrographs only. They also cannot point fully as most optical telescopes but have a feed which tracks across a small region of the sky while the telescope is fixed, a little like an optical Arecibo.
Although La Palma isn't as high or dry as Mauna Kea and so as an infrared site it isn;t as good the 'seeing' or atmospheric distortion is often better and is a much more pleasant place to work because of the lower altitude - although the food isn't as good as on Hawaii!
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