I've had two sets of 26" ST's, one set 2007 the other 2009. Not SX's but the comments apply for the most part.
Both have been great, freehub bushes on this age of wheel do wear out but contrary to Mavic's suggestion that you have to replace whole freehub, you can get replacement bushes for about £8 from ebay sources.
Both sets still true and bearings fine, they are stiff, light and pick up well.
I do regularly put penetrating oil on nipples to keep them from seizing to spokes.
If you do break a spoke they are expensive to replace (£3.50-£4 each) and as there are three different sizes on a wheelset keeping spares on hand is not cheap
The new ITS4 hubs don't have the freehub bush issues as they have a different design.
Will you notice the difference- yes. Not only are the rims lighter and stiffer, the hub bearings and seals have noticeably less drag than Hope hubs