According to my researches (and please check them!!) James Warwick moved initially to Bray around 1882, and then moved to Maidenhead between 1885 (birth of Beatrice) and Feb 1886 (birth of Ernest), although he moved back to Bray again in 1891 and was back in Maidenhead again in 1892 for the birth of his next child! Like most railway companies, if you wanted to be promoted, you had to move around the country, but most would stay within their own company. I should imagine that the depression in the farming industry and the switch to arable led him to give up his job as a herdsman (or perhaps it was betwwe pay, but a more dangerous job. The National Archives might well have his staff records.
Thanks for the info about your father and grandfather - I have quite a bit about the South Moreton ones, although I don't come from that branch.