I've hit a wall with my P5-B - any ideas please ?

specs are E6600 (L624), original ver of P5-B Delux, 11.01 bios, 2 gig 8500 Crucial

9*365 with Vcore @ 1.5 (set in bios), memory at 1090 CAS5, Orthos stable (Blend) for 10 hours

9x370 with Vcore @ 1.52, memory now dropped to 960 so 4:5 multiplier (I've tried both CAS4 and CAS5 to no avail) - Orthos Small stable for over an hour - Orthos blend always fails at about 35 mins, whether RAM set to CAS4 or CAS5.#

normally if I have Vcore set too low for the CPU, Orthos small fails much quicker than Orthos blend, so I'm suspecting RAM or Mobo. RAM I've had up to 1030 CAS4 - so I doubt that.

Mobo voltage settings are ICH to Auto, all the rest in the "pink", can't remember exacts but MCH is 1.45, South = 1.6 etc.

I can't try the x8 or x7 multiplier as my mobo/cpu combination HATES it with a passion - 3.25 gig on x9 only needs 1.5Vcore, but 3.2 gig on x8 needs 1.525 just too boot !

thanks for any tips, Mark.