I went the M Audio 61es route at the time because I was able to confirm from another Hauptwerker that yanking the keyboards from their case was a doable deal. They were also the most reasonably priced at the time and what came out of the case was well constructed and lended itself quite easily to an organ keyboard stack re-make. I also investigated a Casio at the time and it was clear it was not a candidate. I will also admit I wasn't overly impressed with the travel at first but got used to it in short order and now some keyboards with less travel feel a bit weird to me. The 61es action sounds fairly soon in the key travel and I considered coming up with a way of limiting the key travel but have left them 'as is.' Never did get my hands on a UMX610, but is another that several here have confirmed will also go under the knife and come out as a good 'rob it from its case' candidate.
Seems there's always a tradeoff somewhere, you give up this to get that and so on, that or shell out $500 + per keyboard for the real deal. I went budget and it's working.
Marc