Hi mir4ea, at a certain point with too much stuff it's just too much work to get it all drawn in a reasonable time. So that's normal that on particularly heavy projects you have to hide some things or work on some parts separately if your model is extremely large and detailed.

Lots of detail just inherently takes lots of compute time to process.

If you'd like to send me the model file you're having problems with through e-mail (by sending a link using a file sharing service like Dropbox or SkyDrive) I could take a look at it and maybe give some suggestions and also use it as a test case for future performance work.

- Michael