I've just run an interesting 48 hour comparison.  My mining rig runs at about 1460kh/s and I'd been dedicated mining CGB on multipool for about a week.  I was getting about a 0.05 BTC return per day return on profit snapshot.  Got a bit better when CGB went through the roof a couple of days ago.  Exactly 2 days ago I switched back to the multiport for 24 hours and my return dropped to 0.026 BTC a day.  Exactly 1 day ago I switched back to mining CGB and my return for the last 24 hours jumped back up to 0.045 BTC.

What makes this even more surprising is that the CGB exchange rate has dropped ~ 30% in the last 24 hours.  I'm getting about 2 to 3% stales exclusively mining CGB compared to up to 20% stales with the shitcoins.  LTC and NVC are about 1% stales.

Conclusion...  Too much coin switching resulting in down time and too many shit coins with high stales result in lower profitability.