I've got the RS800CX with the G3 GPS and have been using it for sometime now. I really like it, but then, I'm used to Polar products, owning three of them and having used them as part of my sports science degree.
The GPS is amazingly quick to locate the satellites and get a fix - it's the quickest GPS device I own. It's great fun to load the traces onto Google Earth to see where you have been, although, I would warn you that it's not completely accurate but not far off. I find the altitude measurement tends to be the least accurate measure - much better to use the contour lines from a map - I use my satmap active10 to get that information.
I find the memory of the watch is plenty big enough and that's using it to record data every two seconds R-R. I find it is a very reliable piece of kit and it so much better now that you can change the batteries yourself, unlike the older Polar monitors.
The fitness test and optimizer are also useful features, even if the results can be a bit demoralising when you see how unfit you are!
Overall, I'd say go for it - it's a good bit of kit and well worth the money.