Polar to Garmin
2 cents worth...well not really.
Have Polar 800 with GPS (AUD 900). Was great for graphics, altitude, HR etc.
Now have Powertap SL which I ran in conjunction with the Polar.
However now run PTap only, with proprietary head unit, with a view to obtaining Garmin (500 800 something else?). I use Golden Cheetah, which is a vgood (and evolving) freeware, software program (cannot emphasise just how good with great modules).
My problem with Polar GPS was reception, battery life and accuracy of GPS mapping (was good in the open but drastically affected by tree cover etc). I enjoyed referring to data available (but not ideal). Also unfortunate that Polar does not offer Ant+.
To summarize, good choice IMHO. Good luck.
ps Golden Cheetah will accept both sets of data (from both Polar and Garmin) although I guess the 800 will cover all the functions of your Polar).