The difference that you are experiencing colour wise between SVG & PDF is that SVG is RGB and PDF/X is in CMYK and this you have to deal with as your output from the printer will be colour managed by CMYK. Start with turning on "Simulate Printing Colours" from the Window Menu and down to Show Printer Colours, this is only an approx. of what your wet copy from the printers will look like but it is a start. As you have found out after exporting all of your feathering, transparencies and shadows are rendered as a bitmap because they are RGB effects and these effects when exported in a CMYK doc have to be dealt with therefore to show them in a PDF they become bitmaps. If this banner is for print dont use SVG as an export format stick with PDF and since you have AI on your hard drive you might want to do a bit more in Illy than in Xara, like your gradient background?

Like Mike I use both vector programmes in my work but mainly stick with Xara and have no trouble scaling banners and posters so long as you remember a few things:
1. Use layers
2. Always have the Text on the top most layer. You can change the text to shapes if you want as sometimes I's & L's go astray. I don't!
3. Remember there are other ways to do things as Gary has pointed out stay away from RGB effects. You can use them if you factor in your scale ratio to DPI.
4. Use Soft Groups
5. Talk to your printer or I should say, have a conversation with them. They are going to say the file must be this and that if you let me, you must ask can they print this at 100 DPI. and still be readable without too much pixelation.
6. Use all programmes to get the output that you want.