Winter Sleeping Bag - Victorian Alps

I've got some 30 years of hiking under my belt, however the one thing that I have never done, and am developing a serious appetite for, is some winter trekking, as such, I'm slightly oblivious when it comes to some gear. Thinking of a trip to Feathertop this winter coming to see if it is really for me or not.
At the moment, I'm in the process of replacing much of my gear after a break from hiking, have replaced my sleeping bag (for Summer hiking), tent, stove, and a ton more, however I've been of the idea that I will just get a separate winter and summer bag.
The bag that I just picked up is the Marmot Helium (http://marmot.com/products/helium_reg?p=117), a really great lightweight down bag, rated for comfort at -9 degrees, and a damn warm bag to boot. I chose this one as I had been caught out a few times in my VERY old synthetic bag a few times, and wanted to overshoot the mark a little for warmth plus get a bag that helps me travel as light as possible.
So, here's my question. I'm a fairly warm sleeper, I sleep with the blankets off more than I do with them on. With as limited snow hiking experience as I have, would this bag be suitable, if used with a good liner and sleeping mat (I use a Thermarest Neo Air All Season), or would it be a safer bet for me to look into a bag with a higher fill weight?
At the moment, I'm in the process of replacing much of my gear after a break from hiking, have replaced my sleeping bag (for Summer hiking), tent, stove, and a ton more, however I've been of the idea that I will just get a separate winter and summer bag.
The bag that I just picked up is the Marmot Helium (http://marmot.com/products/helium_reg?p=117), a really great lightweight down bag, rated for comfort at -9 degrees, and a damn warm bag to boot. I chose this one as I had been caught out a few times in my VERY old synthetic bag a few times, and wanted to overshoot the mark a little for warmth plus get a bag that helps me travel as light as possible.
So, here's my question. I'm a fairly warm sleeper, I sleep with the blankets off more than I do with them on. With as limited snow hiking experience as I have, would this bag be suitable, if used with a good liner and sleeping mat (I use a Thermarest Neo Air All Season), or would it be a safer bet for me to look into a bag with a higher fill weight?