The MVH500AH is a good head choice for an 85mm scope. It's counter balance spring is set for about 5 lbs and that seems to be about right for the 80-85mm scope range. You can lock the pan, and also add some drag, but there really isn't much need to have fine control over the drag on the pan like there is to control the drag on the tilt. The tilt drag/lock works well. The long plate allows you to get an 85mm scope balanced front to back so that the counter balance spring will work without locking the tilt.
The 502, while very good, is probably more than you need for that size scope. It's counter balance spring is set for about 8.5-9 lbs. The weight of the head is more. One doesn't really need the more refined control of the drag on pan. If you had a larger and heavier scope the 502 might be a better choice.
When a counter balance spring load rating is a good mach for a scope (and the scope is properly balanced front to back on the mounting rail), you can position the scope's tilt, remove your hands, and the scope will stay in that position without having to lock the tilt.
If the counter balance spring is rated too high compared to the weight of the scope, when you position the scope's tilt and remove your hands, the counter balance spring will have enough strength to bring the scope back to level unless you lock the tilt. In this situation you will always be using some force to push against/counter act the spring as you tilt up and down.
Both are very good heads.
