I was just in Lisbon, Sintra, and Porto for about 8 full days. We thoroughly enjoyed it and found we could have used another whole week and more.
That said, Option 1 is pretty much the schedule we did. We had a lot of fun. And, we didn't feel we had enough time ;-).
I feel a bit torn, but it might be that if we are to re-do our trip, I might do 2 days in Sintra and the rest in Lisbon (adding other day trips as desired). If y'all like to walk and enjoy breathing in and feeling the area, I think walking in Sintra is a gem. I think we would have spent overnight in Sintra. Start out the first day early (we did) and leave luggage at a hotel in Sintra, then walk to Pena Palace and Moorish Castle, and walk back to historic Sintra centre and enjoy dinner. Then check in to hotel. The next day, do further exploring of Sintra then return to Lisbon.
Nevertheless, we did not regret doing 4.5 days in Lisbon, 1 day in Sintra, 2.5 days in Porto.
We took the Intercidades (Intercity) train from Lisbon to Porto, and then took the AP (high speed train) from Porto back to Lisbon. The difference in time is only 30 minutes faster on the AP. I found the so-called high speed train comically slow and rickety especially compared to my prior experiences having ridden on the ICE (Frankfurt to Paris), various Shinkansen in Japan, and the Maglev train in Shanghai. AP is not that fast but is called high speed.