FWIW - I understood it was related to payload and VAT too - around the T30 or T32 mark the payload is quite sensitive to upgrades/options/model choices. For instance, you might be able to get a T30 4 motion with DSG and get over a 1000kg payload. Alternatively, you might be able to get a T32 with 4 motion but choosing DSG would take you below the 1000kg payload. You need to look very carefully a the specs and payloads for your preferred model combination if you intend to reclaim VAT from HMRC.
That's exactly it, I did put a detailed post on the other site I'll redo it on here at some point.