Rail vs Air for Heidelberg to Les Fontaines

I'm off to the Capgemini university at Les Fontaines for a training course in a few weeks, and thought I'd check out the rail option. My thought was, if it's competitive in time and cost, I'd go with the smaller carbon-footprint option by rail.

First up, what's to beat: Last time I drove to Frankfurt, queued for security, flew to Charles de Gaulle, followed by a 30-minute taxi ride, all in all about 4 hours door to door. The costs including mileage to the airport, flight, taxi and airport parking are a little over 500 euros.

This time I'll board at my local S-bahn at 16:06, arrive at Chantilly at 21:42, then a 5-minute taxi ride to the chateau. So at almost 6 hours, I'm definitely over the time budget. However the costs are well under control, my ticket to Paris comes in at 124,30. Although I can't know my local train and taxi prices in advance, I'm pretty confident they won't bring me over about 25 euros each way, giving a total trip cost of approx 175 euros.

Added to that, I have most of the trip on a TGV, which is more comfortable than any plane I've been on recently.

So in this case, I'm happy to take the time penalty and use a little less fossil fuel :-)