Virgin haven't fully launched the 360 platform for all customers yet. All new customers get 360 and existing customers upgrading to Ultimate Oomph can get it.
The next stage will be to allow more existing customers to opt for 360, but that's not available just yet.
Also be aware that for 360 it's a maximum of 3 STBs, so you'll have to drop one of your existing boxes if or when you go to 360.
Also the Hub 4 is really for Gig1 customers only at the moment as it included DOCSIS 3.1 support. Some other customers get it where Virgin Media identify it can help manage the cable network performance in an area, but from a customer perspective the Hub 3 and Hub 4 do the same thing.
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I work for Virgin Media - but all opinions posted here are my own