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Go for solid-core cat6. It's more than enough for gigabit ethernet and much cheaper and easier to work with than cat6a/cat7 - last I heard (although I left the industry 18 months ago), cat7 wasn't formulated as a standard and most manufacturers were having problems even passing cat6a testing.
Try not to exceed 90m in one run (unlikely in a house anyway) and get a cheap tester so you're not tearing your hair out trying to figure out why it's not working!
Cat5 cabling... (probably Cat7 these days)
floors are up and skirting being redone anyway, so I guess it's just a case of some plastic conduit under the floor, then run the cable and terminate... any particular considerations?