For your stated needs, a 500/510 is adequate, and less expensive. I have both a 500 and a 800. The only time I've used the 500 since getting the 800 is to compare results on the same ride with each device. The mapping function is okay on the 800. The biggest reasons I got the 800, after having used the 500 for awhile, is to get the routing/mapping functionality. If you have the funds, get the 800/810 - if things are tight, the 500/510 will do what you want.

And, yes ... Strava is "better" for monitoring your progress. I have one "standard" loop I ride that is 15.2 miles with about 900 feet of climbing. My goal is to ride that loop in a certain time, so I defined a Strava segment of that loop. It is very simple to compare results of that ride with one another.