All contracts are 4G but you can ask if it's enabled on your account @Coazin
As for speeds, the website will not consider thickness of wall, building structure or signal connection if there are buildings etc in the way
It's always best to try p&G sims before committing to a 2/3 year contract
If you are within 28 days you have a change of mind option and can return the phone and sim card
As a telecoms engineer you'll understand bandwidth or rather the lack of it allocated to O2 when compared to EE.
Add to this mast congestion and O2 speeds drop dramatically. If you try around 2.00am when everyone is in bed, you'll probably see a significant increase.
Honestly, if you are in a busy area / large town or city, you are better off with EE from a speed pov.
They are working their way around and supposedly upgrading the worst areas first.
All will be done eventually, but that could take some time.
Track usage, upgrade and get support with the My O2 appDownload My O2