Hi Fergus,
Our fleet of 767 300s has both winglet and non-winglet aircraft and we regularly fly both. We use them for both long-haul and short-haul. The only differences I've noticed on normal revenue flights are the winglet aircraft are more slippery. If you need engine anti-ice in the descent its almost certain you'll also need speedbrake with a winglet jet. The fuel economy on long sectors is also better with winglets, less so on short sectors, probably due to the extra weight of the winglets not being offset by the lower drag on a short flight.
The fine differences in roll stability and cross wind landing behaviour are not noticeable in line flying. They probably exist but you'd need to do a test programme between identical jets apart from the winglets to find out. The biggest differences in practice are between flying a heavy jet (180000Kg) or a light one (100000Kg). Landing, we have the option of F25 or F30 landings (Company prefer F25 unless good reason for F30) which make more difference in handling than winglets or non-winglets. There is no difference in cross wind limits and I haven't noticed any difference in behaviour. Not to say there isn't any but to notice it you'd need to land a winglet jet, then land a non-winglet on the same runway with the same conditions. That obviously never happens in normal line operations.
Sorry that doesn't help your thesis much but best of luck.
Last edited by Beakor; 17th Oct 2012 at 08:37.