The difference in height is the same as the difference between the recorded height at the start and the end of the ride. I think this is to do with change in atmospheric pressure over the two hours of the ride.  Or it could be that the Green feels like it is higher when the end of the ride is uphill and the ride has been hard. Obviously more research to do here and Debs has kindly offered to help with the data analysis although she recons it can all be done by feel . 
   

As for plotting routes, Google Earth is OK (they call their routes tracks) and has the advantage that you can save/export to Google maps and others. I have not really used others as I have Tracklogs.

Just to prove that we usually earn our time in the pub, and to answer question from Polka, here are the ride stats for the Thursday rides I made it to in the last two months. Stats are from my Garmin 705 using a donateware software package called SportsTracks that stores GPS and heart rate data. Interesting to see the difference in the moving time (>3 km/h) between rides. I have data back to June 2008 if anyone has trouble sleeping!

Date              Location       Time       Moving Time Climb (ft)            Distance (km)  Speed (moving km/h)
03/09/2009   Capel         01:42:00    01:11:14   +1,591 / -1,658     20.2                17.0
10/09/2009   Saltwood   01:55:13    01:23:27   +1,835 / -1,799     24.7                17.8
17/09/2009   Saltwood   02:04:05    01:32:06   +2,169 / -2,075     26.8                17.5
24/09/2009   Saltwood   01:56:00    01:25:02   +1,753 / -1,725     24.9                17.5
15/10/2009   Saltwood   02:07:23    01:24:56   +1,856 / -1,869     23.0                16.3
22/10/2009   Saltwood   02:00:30    01:44:07   +1,785 / -1,902     31.5                18.1
29/10/2009   Saltwood   01:56:50    01:36:01   +2,051 / -1,990     25.5                15.9
Total                               13:42:01    10:16:53                                176.5               17.2

Nice ride last night, I really enjoyed the new bits in Sandling woods and am sure that I would not have done them in daylight. As a 'Garmin boy' I can report the following ride stats:

Ride time: 2:07
Moving time (speed >3km/h) 1:25 thanks to the stiles
Distance 23km
Height gain: 1856 feet
Speed: 16.2 km/h

Nice ride last night, thanks all.

The stats for the ride are below, not long but a bit quicker than average which must be why my legs felt tireder than usual. Rev is you send me a PM I can let you have the GPS trace.

Distance: 15.37 miles (24.73 km)
Climb: 1753 feet (744.31 meters)
Elapsed Time: 1:48:49
Riding time: 1:26:04
Avg Speed: 8.5 mph (13.6 kph)
Moving Avg: 10.7 mph (17.2 kph)
Max Speed: 28.0 mph (45 kph)