Have a 2006 Striker R1 and looking to change the filter and oil. Where do I buy and best oil to use? Will be used for trackdays very soon so would ideally like to buy a few filters and do a change more often than not.

I use Mogul 300v in my 5vy from Opie. Not cheap but the best available. It's full double ester syn (not had any issue with syn). Have it on fairly good authority that it's used by most superbike teams irrespective of sponsorship. I use 5/30 but have used 5/40 before but level drops a lot more when cold as drainback to sump is slow (level light can do.e on if you received too high too soon).

I've used in the past...
Valvoline 4t; ok but frothed a lot at high revs (you can see it in the level window and the level float sinks and puts the light on).
Silkolene comp4: ok still frothed but better and switched to Motul on engine builders advice.

Took your advice and used the Motul, see how it goes at weekend at Pembrey