The Brit Lancers would probably make good Turks for Mespot and Palestine. Some of the helmets have more of a Turkish look about them though it is always hard to tell from photos. Brit cavalry equipments changed. Why on earth did they keep changing they should have kept the good old Nappy/Crimean uniforms until they wore out .
The Wolseley helmet is the big difference. A good Wolseley helmet on a 1/72nd scale figure is needed. Infantry initially had 1903 equipment but webbing a little later on so 8th Army figures could be looked at. Most cavalry (and yeomanry) units fought as mounted infantry. British Lancers were in the Desert Mounted Corps of 1918 - a lot of horses and some camels in this formation.
Bengal lancers is a broad term and indeed regiments of Bengal lancers would have looked different. Typical is the 9th Lancers Hodson's Horse which fought at Megiddo and Damascus. The "Bengal" was dropped in 1903 but the 9th is a Bengal Lancer regiment. They often fought and rode in their undershirt as well as their tunic and the horses had a lot of baggage on them.
Figures of Indian infantry are sadly lacking but to consider both Mespot and Palestine without them would be like missing out at least half of the allied army.
As my intention was to build some more colourful units in WWI from the future Strelets colonial range, you have rightfully dissuaded me from doing so, at least for the sets I thought I could cheat a bit. But turkish cavalry out of the british lancers is a great idea. Thank you so much.