If you're using BMW recommended oil, I'd extend the drain interval instead of shortening it. 7500 is a good change interval unless you're driving at the track or hit >260d oil temps regularly. 3k would be a waste of oil and money imo.
2007 E90 335i, TiAg, 6AT, ZPP, ZSP, ZCW, 6FL, HD
Quaife lsd, ETS fmic, GIAC s/w, Dinan intake/exhaust/oc, KW/GC/M3/Meyle susp, Apex Arc 8, Mich PSS