A standard T-303 will normally cruise at approx 170 kts with a 24”/ 2400 rpm power setting at 10,000 ft. With the stc the cruise speed will increase to 190 kts if the aircraft has boots and 191/192 kts without boots.
Yes, but you will burn a lot of fuel. No experience of the STC, but my T303
has been across the pond to Montreal and back and from London to Georgia
(ex Russia, not USA) and back in the last two months.
A very versatile aircraft.