The 450 is as reliable as any Yamaha
I have owned in the past. The maintenance is a bit more difficult with the aluminum frame as everything is pretty tight for space to work with. I feel that the 426 was a much better engine and tranny package in the lower part of the RPM range, but this bike flat out rips when you are in the middle and upper stages of the engine. The '07 turns much better than the old 426 and the weight, while not really any lighter , is a lot lower in the chassis so it feels better. I have had the suspension done for my weight and riding style and that was a huge improvement over stock. I added 1 tooth to the rear sprocket and it seems to have covered the spot that I felt was weak off the bottom. We ride mountain single track here so there are very few wide open areas to get into 5th gear for any length of time, so I don't miss any top end I may have taken away. For the break-in period, I just warmed it up and ran it at different loads and RPMs for the first 10 minutes and then rode it like I stole it. The piston rings need to have that load on them for break-in so they will create the seal to the cylinder wall that they need for the engine to have all the power it can produce. A few oil changes early with quality oil and filters will give many years of service life. I should note that I rarely ride in the uppermost RPM band, most of my riding is in the lower to upper middle RPM's. High RPM riding will require more diligent valve servicing. Good Luck and have Fun! -- WR Dave.