Just my own observations, so do what you are inclined to do. But you asked so here's what I found in over 120,000 miles on various Harleys since 2004. Every one of them had the 1000 miles done by the dealer at or before the 1000 mile mark. The earlier ones were HD dino and the last 3 were the recommended synthetic in all three holes. By 3000 miles I put either Mobil 1 80w 90 gear oil or most recently Spectro 6 speed oil (which is 75-140) and either oil makes shifting smoother, quieter, far less fifth gear whine in the six speeds. Easier to find neutral and the operation doesn't change but very little in 10,000 miles I run between trans oil changes, nor a significant change in 100+ degree outside air temps. With the HD SYN 3 the bike sounded ugly in hot temps and stayed that way until you changed it. Every shift gave a metallic tink. Shifting started getting louder and more metallic by 3000 miles with HD crap, dino or SYN 3. If it was very hot outside air temps even quicker.
I bought the wife a FLHXXXtrike last August 09 and she had a helluva time ever finding neutral when new and after the 1000 mile maint with syn 3. At 3500 I did the maint myself and added Spectro 6 speed oil to the trans, Mobile 1 V-twin 20-50 in the other two holes (6.50 a QT from the Distributor) and she has NO PROBLEM at all finding neutral and even though this was her first bike/trike ever to operate she asked what I did that made it so much quieter and easier to shift. Oh and I only change the mobile every 5000 and the Trans every 10,000. By the way she has 12600 miles on it now. I couldn't wait to get the SYN 3 out of any bike I had it in by 3000 miles as it got so darn noisy and changed so much with heat I hated the stuff. Will the SYN 3 make your bike wear out faster? I doubt it, but I just don't like the feel of operation nearly as much as the Mobil and Spectro combination. It makes me feel good!