Way off the orignal topic I know but still relevant to the benzene issue.
Benzene is also found in petrol. Whilst you (hopefully!) won't be drinking petrol, there is still the possibility of exposure via fumes from unburnt fuel and also if you get petrol on your skin there will be some absorption.
Premium unleaded (95 octane) contains more benzene than regular (91 octane) unleaded. 98 octane petrol tends to contain more than either. Whilst this isn't a problem when it's burnt (since the benzene burns) it's not a good idea to be handling petrol more than absolutely necessary.
If you must handle petrol (eg when filling the mower) then it's best to use the LOWEST grade that's suitable for the engine in question. For 2-stroke Victa etc mowers regardless of age regular unleaded mixed with 2-stroke oil will be fine. They don't have valves in the engine and never needed the lead.
For pre-1986 4-stroke engines (including car engines) it's safest to add "flash lube" or similar to guard against valve damage from using unleded fuel but in most cases there's no need for premium with mowers etc. Some older cars do need premium however.
If you run the Victa (or other) 2-stroke on premium then you'll end up breathing in quite a bit of benzene since there is always unburnt fuel in 2-stroke exhaust. Not good for your health. Likewise chainsaws, brush cutters, whipper snippers etc with 2-stroke engines. Some outboards do need premium though.
If you want a high octane petrol with low benzene content then an ethanol blend will do the job since the ethanol is an octane booster. It's generally preferable to use non-ethanol blended fuels where possible in 2-stroke engines however (since the ethanol can impair lubrication in these engines).