I've never ridden a V with soft bags but I have ridden mine with no bags and with hard bags, no vibration difference at all, and very little handling difference. The advantage of side bags (boxes) over a top box is side mounted luggage doesn't effect handling as much as top mounted luggage.
The advantage of hard luggage is security and generally convenience of accessing, while soft luggage is lighter and less expensive.
Givi or SWMotech, either one is good quality and won't fail you. I bought SWMotech EVO racks and I've been perfectly happy with them. I got them because I liked the quick disconnects but I never used them so I replaced the QDs with bolts, it was a feature I never used.
As for aluminum or soft, don't forget about plastic hard bags. It really just depends on what floats your boat. I like plastic hard bags because they are secure and lockable and relatively light. I had Givi E21s until recently but needed more storage so I just got a set of Storm boxes.
I think another question you may want to consider is top load or side load. Your lid type may be the determining factor for what material your chosen bag or box is. Alum boxes are generally top load which can be convenient to access unless you are carrying luggage across your seat. The 4 week trip you describe may very well require an additional bag thrown across the seat so something to think about. Most of your hard plastic boxes are going to be side load, with the exception of a couple Givi options, a Pelican box and another brand that I can't recall.
Last edited by ray h; 12-30-2014 at 11:10 PM.