My searches are mostly showing inbound int'l connections involving clearings customs, so if anyone has any experiences that would be helpful :-)

I'm looking at two flights from SJC to LHR, one via DFW and the other via ORD on a Thursday evening.

The DFW flight arrives from SJC at 8:25PM and departs for LHR at 9:05PM, giving me 40min. The whole iten is $867

the ORD flight arrives from SJC at 7:40PM and departs for LHR at 8:15PM, giving me 35min. The whole item is $840

Both seems a little tight to me. Does anyone have any recommendation on which one is a better bet, taking account the time of day, delays, gate location and whatever reason you can think of?

I saw the Wiki and looks like both connections meets the bare minimum connection time, so at this point I'm just wondering which is the safer bet.

Thanks!