once a season which ever comes first.... My car is not a daily driver and I put about 5k or less a year on it so I am usually changing once a year... The full synthetic oil should go 7.5k without a problem with the Maserati filter but I would change it no higher than 5k miles, as the filter usually clogs up around 2500 miles and goes into bypass mode anyway according to studies done by several companies.
Agree with what Mark has said above. I would say 5K to 7K max or yearly, whichever comes first, and go for a quality, full-synthetic oil. In the UK you could get Motul 300V or Silkolene Pro S... I do source mine from Opie Oils, www.opieolis.co.uk, which provide a second-to-none service. With oil change comes filter change. I do also replace the spark plugs, Denso's being my choice and recommendation.