Barlowing Zooms

I'm wondering what kind of experience people have had with barlowing zoom EPs. Lots of glass , I realize. But what are people's thoughts?
I just bought a 80mm Apo f/7, and was wondering about using a zoom , both barlowed and not, as part of a grab and go set-up. If I was to get something like the Speers 5-8, I could also use it as high power double star EP for my 8" SCT.
A Tele Vue Zoom is probably out of my budget and couldn't be used with my 8".

David

I've tried my SW5-8 with the Shorty Plus 2x and the Antares 1.6 and noticed no degradation in the images with either.

Popular belief is that more glass reduces brightness and/or contrast. Background brightness changes with the barlow due to the mag change, but I've looked for changes in contrast with a variety of barlows and eyepieces, but haven't found any when using decent quality barlows. I have used some low quality shorty barlows that muddied the view a good bit, but did it uniformly with every eyepiece regardless of the number of elements they had.