Speed tests vary depending on where the servers are (obviously). The speed test here on TBB right now: 832(dn)/909(up), and Ookla 916(dn) / 924(up). It also depends on equipment. The Giganet router had no problems with speed but I don't use it as I like more control and have quite a complex network setup internally with a couple of servers, multiple Lan-Lan VPNs and backup connections - not your typical "resident!"). My old (Vigor) router struggled to maintain >800mbps esp with IPv6 enabled, but my new OPNSense box is pretty powerful and has no such problems.
But do be aware, your not going to see gigabit speeds everywhere, for example, xbox game downloads, don't appear to be much different from my previous 350Mbit virgin connection likely because Microsofts CDN limits speed per connection etc. But I can do more at the same time as downloading that >50Gb game. I do sometimes wonder if its worth having more than 500mbit but its nice...
Decent upload speeds and stable latency/jitter is probably more important to me personally (Virgin being diabolical on that front). My pings on giganet are nice and low and stable even under load typically 5ms to bbc.co.uk (ipv6 which is interesting slightly lower latency than IPv4 - that may be my equipment) - it will depend where you are in the UK I guess - I'm not that far from London.
There is also the fact that its a contended service as is all residential broadband. There are 20 properties on my street with one cabinet and the CF network as a whole is brand new still with (too) many roadworks around

. Right now I think (complete guess) only 3 or 4 of us are using CF on my cabinet - so I do wonder how it will degrade as more people join up.
I think, to most people, the impact of the difference between 900 and 1000 is relatively insignificant (compare to the massively noticeable difference between 10 and 110 mbit for example).
As for wait times, I'm not sure I can answer that with any certainty. I only had a choice between two ISP's Giganet and Zen here at the time (there are more now), I don't think there was much difference although I think I waited longer than 8 days (and I'm pretty sure I was aware it would be longer than that when I ordered). Giganet at the time gave me the impression that I was one of their first customers in my area (CF had only lit the street a few weeks prior and Giganet implied that they were still running tests in the area before installations could begin - not sure how accurate that information was!
They (giganet) do not use their own installers - it was all CF's contractors (Kellys Coms) here, same when the parcelforce van destroyed the cabinet, kellys were the ones to investigate/fix it.
Giganet 900 (CityFiber), Protcli VP2410 running OPNSense and Three 4G Backup