That's a good question. I have just ordered a Samsung Pro 90/80MB/s 64GB and was thinking about the same.
I think it depends on the App, the speed/performance of your SD card, and the durability of Lumia SSD storage. So far, I have been thinking 3 scenarios but that's not final yet .
1- Non data-intensive Apps will perform almost the same and should be installed on SD card. Apps for try-and-decide should go to SD card in trail period too.
But there is 2 different scenarios for data-intensive Apps ( Apps with intensive Read, Write, or Read/Write requirement):
2- Read-intensive Apps will preform much better on internal storage, without degrading the SSD and should be installed on the phone.
3- Write-intensive and Read/Write-intensive Apps, including those with a local database, will perform better on local storage too. But there is catch 22 here, the intensive Write can create a lot of wear and tear on the local storage and degrade it over time.
I don't know much about the durability of Lumia's internal storage, but they are SSD drives. As a general rule, a SSD can Read almost for forever without any problem, but have a limited Write-cycle. Intensive Writing will degrade a SSD and kill it over time.
So I'm still keeping the last scenario (Apps with Intensive Write or Read/Write requirements) open. maybe somebody else can shed a light on it.