Hello,
I downloaded and installed Dorico 1.0.10 (demo) yesterday. As I consider leaving Sibelius (I have been loyal to it since 1998), I wanted to test the software with my current work, which has about 16 staves and 3000 measures. I exported the file from Sibelius as XML and imported it in Dorico. First, it took about 4 minutes to import, but even when I then saved it as a Dorico file, it still takes about 3-4 minutes to open. The score makes the program very laggy. Even playback takes about 2 minutes from when I give the request until the music starts playing. My computer is a Mac Pro (8-core 2009) with 14 Gb of RAM and a solid-state hard drive. Sibelius is almost instantaneous in opening and playing this score. Also, the Dorico file of my score is about 6 times larger than the Sibelius file (from 2 Mb to 14).
I LOVE the new approach to notation and writing of Dorico and believe me, I am READY to leave Sibelius, but the slowness of the software makes this option not possible at this time. Any suggestions?
Thank you,
Jorge
Jorge, please send me your Dorico project so we can take a look at it. You can zip it up and email it to me at d dot spreadbury at steinberg dot de.
As things stand I don’t think these timings are exceptional. I just tested a chamber piece of 1800 measures. It loads in 4 seconds in Finale and when converted to a native Dorico file it takes 2’40" to load and becomes painfully slow to work with, even on a pretty fast i7 with 16GB. Cudos to Dorico for importing it flawlessly though! When trying to reimport it into Finale 25.1, either Finale gives up without any warning or reports that the file is too big! 
Personally, I’m fully convinced that these issues will vanish as Dorico matures.