GUI with alpha sprites performance issues

[Grim]

I have a simple question (I apologize if it doesn't qualify for a new topic, but I really need to know this):

Do alpha sprites in GUI cause more slowdown than if they were used as a room object?

I'm thinking of using GUI for a noise filter for the game, but not sure if this is a good idea, due to performance issues.

I've also upgraded TCL interface slightly, so now text labels are displayed on a alpha sprite with transparency. If GUI is not visible most of the time, does it affect performance too (as if it was constantly taking up  memory)?