AMSOIL is excellent, as is their filter. Just make sure you don't get their newer budget oil which is rated out to 7500 miles only.
The subies factory suggestion is 7500 for 'normal' driving oci's. With a good synthetic oil and filter you should have no problem going long even with normal 'spirited' driving.
For peace of mind, run the first interval with AMSOIL to 6000, then go 7500 and get it tested at Blackstone Labs.