I saw that your enquiry hadn't received any comment as yet so felt that I should let you know that the subject of British officers in the Egyptian Army is of some interest to me as well. We have already corresponded on " another " Forum so you know that I collect and research the Egyptian Army of the 1880's.
Henry Keown-Boyd's excellent book Soldiers of the Nile is the standard reference on the subject, as I'm sure you know, but, like, any other reference book it is unlikely to be 100% definitive. I was lucky to have a wee book published several years ago, an annotated medal roll of awards to the Commissariat & Transport Corps in Egypt and the Sudan and I know that I missed a few names. Although I managed to describe the medals awarded to about 2,500 officers and men I know that there are a couple of soldiers who " missed " a mention in my roll because their medal roll hasn't survived or because some insect devoured the bottom of a nominal roll. Mr. Keown-Boyd admits in his forward that he may have missed a few officers and I have probably identified two or three men who eluded him, which is pretty darn good considering he describes 1200 in his book. Those British NCO's who were commissioned from the ranks directly into the Egyptian Army, 'though few in number, were poorly documented and were easily missed. Only their campaign medals attest to their Egyptian service.
No doubt you have read the better known sources, like Under Crescent and Star and, of course Churchill's writings, but I would heartily recommend finding a library with a complete run of the periodical " Sudan Notes and Records. " Dozens of British officers who served in the Sudan with the Egyptyian Army or, later, with the Sudan Defence Force, contributed articles on military operations, zoology, biology, tribal traditions, etc. and countless individuals are mentioned and/or described therein.
Living as you are in the UK, you aren't far from some great regimental and corps museums. You're another medal collector ( like me! ) and The Buffs Museum in Canterbury displays the magnificent awards of Major-General B.R. Mitford, an old Sudan hand, while places like the RLC Officers' Mess in Deepcut have a breathtaking Medals Room that has most combinations of clasps for the Egypt Medal and the Khedive's Sudan Medal. The RE Medals Room in Chatham houses medal groups from a number of young Sappers who dug wells and built railways across the Sudan and it is well worth a visit. Should you ever find yourself in central Canada then I would welcome you to view my own modest medal display. No VC's I'm afraid but I can guarantee some interesting conversation over a drink, or two.
My apologies if I'm telling you things which you already know. I'm sure that many other members of this Forum have special knowledge and/or experience on which you could draw when the occasion arises. Please feel free to contact me if you think I can be of any assistance with your research.