Firsthand experience in .243? No.
But I have used VV powders for a long time, at least as far back as 20 years ago, and still use several of them. I use N110 and N120 in smokeless muzzleloader, N133 in 6.8 spc, I have used N160 in several things, and use N565 in my .280ai.
Also, I use GRT for a lot of things and have done so for several years now. It is not perfect. All models are incorrect; some are useful. GRT has always been useful to me and if it says that one powder will perform better than another in terms of max velocity I generally believe it to be fairly accurate. Also, where it errs, the errors are often attributable to variances in cases or throat lengths, etc, and at least generally, if GRT says I can hit a certain speed with a certain powder/bullet, I can do so, though I may need more or less powder to do so. It has also taught me the importance of seating depth to pressure and velocity, which I freely admit I didn't really understand for a long time.
Based on this info below I'd look for some N560 if I were you. I've never used N560 but I can tell you that N565 is great in my .280ai; it makes more speed than IMR8133 did with the 180eldm and once I got to that point I didn't even push load development anymore. No need. Those things fly well enough to kill stuff bigger than I shoot, further than I shoot.
Anyway - worth what it cost you - here's a comparison to some of the powders mentioned in this thread, with the 243/108:
ETA: I bet N565 would work too but while I don't mind compressed loads at all, I have found that sometimes what looks like an awesome combo on paper ends up not working because I can't stuff as much powder in the case as GRT thinks I ought to be able to, even if I adjust the model's case volume to match my own.
