I'm afraid I'm probably going to have a lot of questions in the coming months...hope you can put up with me...here's another one.

I've got 4x green screen tracks - (no fx or compositing at all), two basic .psd cloud images with transparency layer and gradient (to be part of background image) - one with a composite envelope on it and the other without, and two .psd colour gradients with transparency (to be other part of background image) - one with a composite envelope on it and the other one without.

When all these tracks are unmuted, the video play back is terrible...unbelievable

To try and find out what was causing this extremely poor playback I went though and muted tracks until playback became normal, and found it was the colour gradient tracks. Switch them off and playback is perfect. Switch them on and it stops...

Why would colour gradient tracks like this sabotage playback?

...Why would colour gradient tracks like this sabotage playback?
Don't really know, as I've not used psd tracks much. Never got in the habit. Have you tried png with transparency? Vegas seems to like png...

The other thing is to take your imagess down to simple .jpg at the resolution of your video. Generally get it to 1920 x 1080 for HD. When you have a huge file Vegas has to convert down for each frame anyway, and your image is not going to have any more resolution than 1920 x 1080

Thanks guys.
Four gradient files sizes were (.psd) and now are (png):

File 1: psd 4371x2400 pixels = 18.7MB, png 1000x549 = 27.9KB
File 2: psd 4371x2400 pixels = 32.9MB, png 1000x549 = 223KB
File 3: psd 4371x2400 pixels = 27MB, png 1000x549 = 161KB
File 4: psd 4371x2400 pixels = 13.7MB, png 1000x549 = 21.1KB

Cloud files:

File 1: psd 4371x2400 pixels = 19.6MB, png 4371x2400 = 915KB
File 1a: psd 4371x2400 pixels = 19.6MB, png 1000x549 = 156KB
File 2: psd 4371x2400 pixels = 19.7MB, png 4371x2400 = 929KB
File 2a: psd 4371x2400 pixels = 19.7MB, png 1000x549 = 162KB

To make a stranglehold on the obvious, the file size reductions are significant...

With these files now replacing the other ones (Gradient 2 and 3, and Cloud 1 and 2), the playback is normal.

Given that I am not using HD and my video resolution is 720 x 576, should I make the image sizes the same? Is there any reason not to?

Borrowing from graphic designers' workflow, if you aren't zooming in on these images, roughly double the project pixel dimensions is a good guideline. So, following this would be .png at 1440x1152.

The reasoning is that any slight resizing would start from a higher resolution.

But I've never really done a direct comparison with 2:1 vs. 1:1.

Borrowing from graphic designers' workflow, if you aren't zooming in on these images, roughly double the project pixel dimensions is a good guideline. So, following this would be .png at 1440x1152.

The reasoning is that any slight resizing would start from a higher resolution.Good point and helpful...I am resizing sometimes...reducing the image by about 1/3rd.