Not only will your gains slow to a crawl after 8 weeks but chances are your sides like elevated BP and a retarded lipid profile will worsen the further you get in to the cycle.

You're better off cutting your cycle when gains slow and/or when sides worsen whether it's 6 weeks or 8 weeks, and then taking time off to recover and start again so you can experience rapid gains again instead of prolonging a cycle that's doing more harm than good..