The question at hand is "when" to change to synthetic? But the underlying question is "should" you change to synthetic?
There are two reasons to run synthetics; extended OCIs, and temp extremes. Some would contend that wear protetion is a reason, but that is covered in the concept of extended OCIs.
If you're not going to extend your drain intervals, then there's little, if any, benefit to synthetic. And I don't buy into the whole "synthetics are better than dino's at temperature extremes" here, becuase no sane person is going to start up his motorcycle below freezing, so cold pumpability is just not an issue. And since this bike is liquid cooled and fuel injected, I also don't think that any rational person can argue that it's just "too hot" for a dino fluid. Assuming it's operating properly, a thermostatically controlled engine is going to run at 190-210 degrees F, regardless of where you're at or what you're doing.
For those that are doubters, I offer the experience of my friend in D.C. that currenly has 109k miles on his ST1100, running nothing but the dino GN-4 Honda oil changed every 8k miles. Honda oil certainly isn't "special", if you've ever seen a UOA; HDEO's are far better than that stuff. My point here is that he's run that far on what I consider to be low-grade dino stuff with run-of-the-mill filters. The SV-650 is probably no better or worse in design and build than the Honda. So, considering oil choice, don't tell me that dinos can't make a bike last.
You've bought an excellent little bike. That engine is very stout, and well designed. Reliability has been very good with that SV-650 based engine.
If you're going to OCI at or less than 5k miles, on the V-strom, there is no real reason to use synthetic in the first place.
However, if you're convinced (emotionally, and contrary to the facts) that you "need" to run synthetic, then I'd say switch whenever you want to. The reality is that it's not going to effect that bike positively or negatively to any degree that you (or it) will be able to discern, in daily operation. Just be willing to admit that you WANT synthetics, not that you NEED them.
The bottom line is that synthetics are not about making a piece of equipment last longer; it's about making the lubricant last longer. And if you're not going to extend your OCI, the point is just simply moot.