For regular oil use Castrol GTX 10W30. I've been using that stuff for years and it really lasts. Even when revving the crap out of my car I get respectable milage on it between oil changes. BMW also recommends using Castrol GTX
Also, using synthetic oil on older engines will only make your oil burn away faster. Stick with the cheaper regular oil as it's thicker and won't burn as easily.
'02 Mercedes C32 AMG 3.2L Supercharged @ 18psi - 341WHP/358lbs*ft TRQ (DynaPak) Eurocharged custom tune, ASP 178mm crank pulley + PSK, CM30 i/c pump, i/c iso kit, Magnecore wires, NW CAI, dual custom exhaust, H&R sway bars, H&R SS coilovers, KMAC camber kit, H&R spacers, Quaife ATB LSD, goodridge SS lines, Porterfield RS4 pads, AMG 18" rims, AEM UEGO wideband, Dashdaq datalogger, Kenwood Excelon DNX8120