Offroad Tyres for GU IV 3.0TD

I have a set of near new 16 x7 Prado rims shod with 245/75 Cooper ST's I was hoping would fit on my new GU as a spare set for off-road. Despite being a little under tyred I figured it might be a cheaper way to go, rather than selling and repurchasing slightly bigger wheels/tyres.

Well, the Prado rims don't fit, so the expensive option of selling and rebuying looks the only option.

What's the feedback on the new Coopers STTs (not the radial) for this truck as a dedicated off road tyre for trips only (I will use std wheels & rubber for commuting)? Not sure how I would justify an invoice on my lease operating costs which says - "Mud Terrains", as opposed to Cooper STTs which is nicely unidentifiable to the Admin person at work. The new STTs on appearance appear to be a good interim position betweeen the STs and a Mud Terrain. Perhaps someone who has gone down the lease path before can advise if this is an issue at all. Would be used for general off road touring, high country, typical club trips etc.

I have listed the Cooper ST tyres and rims under the Exploroz Wheels & Tyres section if anyone is interested. Rims were new when I purchased them and are in perfect condition. The tyres have done only one trip up to the Murray and have less than 1,000km on them and are similarly in perfect condition.

Any advice offered on lease and/or tyre selection options would be appreciated!