So following the extremely useful instructions here I have to managed to successfully disable the discrete graphics card on my 15" MacBook Pro 2011. The laptop which was getting stuck on boot screen with stripes and such is now starting up.
However, I see strange things like blackened Safari tab titles, Finder tabs, occasionally chunks of webpages disappearing only to reappear on scroll, etc. All of these point to graphics problems.
Does this mean either the integrated graphics chip or something else on the logic board is starting to go kaput?