Everything Ian said. Also, if you end up doing more than a couple of weekends away, you will almost certainly find that the niggles with soft luggage will make the extra investment in hard luggage seem worthwhile, and you'll end up selling your soft luggage. I'd recommend going for the cheapest possible, trying it out, then making a decision on whether you want to spend money on better soft luggage or save up for hard luggage.
Also, take a few extra bungees and some Gaffer tape in case anything goes wrong. On one trip, a mate's bags got a singeing from his Ducati's exhaust. We stopped at a tea shop, scrounged some tin foil, and wrapped it round the exhaust - worked fine for the next 10 days!
Brief rant about Oxford - don't be fooled into thinking that the Lifetime range means a lifetime guarantee. When the zip came unstitched on my Lifetime tank bag after 5 years or so, they refused to honour the 'guarantee' because I didn't have the receipt. I tried to point out that 'Oxford Lifetime' was embroidered into the product, so a receipt should hardly matter, but it fell on deaf ears. Lesson learned, Oxford boycotted.