Normally, I would agree with the above, however, you said that you managed to get a 1.6 60ft with lower tyre pressure but your clutch slipped.
If you manage a full run with a 1.6 60' you will get into the mid 11's. However, this might prove diffcult to always replicate.
Either way, as stated already, smaller diameter tyres with grippier tyres will definitely improve your times, And with more power, a 10 is definitely possible.