The way I understand things, is the process for taking your pension while still employed by RM is slightly different to being a deferred member. So leaving after you've started the process might put a spanner in the works and you may have to wait longer to get your pension?
Perhaps something to ask the PSC and Capita, unless someone else has personal experience?
You'll get options forms from both the RMSPS(Capita) and RMPP(RM's PSC).
25% can normally be taken tax free, but the DBCBS muddies the waters as that can be taken as part of your NRA65 or separately.
Basically, if you want the maximum lump sum possible, you can take a 25% lump sum from both the main pension and from the DBCBS, and therefore the reminder of the DBCBS will be paid as a taxable lump sum. Although as that will come under normal PAYE rules, how much tax you pay will depend on other income.
But if you want to use the DBCBS to provide the NRA65 lump sum, you'll get a bigger pension in return.