Adam, i have had no experience with savage exhausts so cannot help out in this area sorry.
Regarding powerflow exhausts, i have one, are fantastic I would say definatly worth it. I reckon the savage would be quite loud, like a typical 1L Corsa with big bore exhaust sound, as a few guys i have seen with their corsas fitted with a similar exhaust. At least with powerflow you can specifiy what sort of sound your after and could make it to your personal spec. Also if you go for a powerflow, at least get the flexi pipe change, or a cat back like mine, fantastic difference and sound, lots of pops and bangs

Fitted was £270 FYI.
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Powerflow Cat back and flexi
Powertec SL1 induction kit
Eibach 35mm springs
10mm Rear wheel spacers
Crankcase breather
Red hose covers
Stainless Steel engine bling
Gloss black grilles
Red calipers
Plus much more ebay items