IMO you've already found your new revolver, that price is not at all bad for a 4 inch 686 in good condition. What you will get is a revolver that was specifically designed for the 357 Magnum. This means that it's strong enough to tolerate lots of shooting with 357 Magnum but there isn't any excess weight like there would be with a model 27 or 28.

BTW, not knocking the larger N frame models because IMO they feature the best triggers on the planet. However the N frames do carry more weight and also command a higher price.

Sum it up and that 686 is a perfect fit for what you are looking for. BTW, while that long barreled model 29 is very cool looking they are also SLOW sellers on the used market. To put it simply you'll find it difficult to get a "fair" price for an 8 3/8 inch model 29 because so few people are out there looking for one.