It's between 4 HP/ 252 Def/ 252 SpDef Calm and 4 HP/ 252 Def/ 252 SpDef Bold on a Rain Stall team. I have a bunch of stall teams, and each of them that use Chansey/Blissey are using one of those two spreads, but I thought about if Chansey/Blissey really needs to be able to take physical hits or should focus on taking heavier special hits because of how top heavy the metagame is. I guess we could say I need it for Latios.
Are you running a rain stall team without Ferrothorn? Just wondering, Ferrothorn is often used on rain stall and checks Latios.
Anyway, lets break this down.
For Chansey, the Calm spread I suggest is 112 HP / 252 Def / 144 SpD, which avoids a 2HKO from Latios specs Psyshock, with no rocks on the field. If you want to run a more defensive spread to take it with rocks, keep in mind that 252 HP / 252 Def / 4 SpD Calm in inefficient compared to 4 HP / 252 Def / 252 SpD Bold which takes less damage on both fronts. For a bit more bulk 180 HP / 252 Def / 76 Calm avoids a 2HKOed by Life Orb Alakzam Psyshock after rocks.
So pretty much your Bold spread takes everything you would ever want it to take outside of specs-Psyshock from Latios after rocks.
If you want to take Specs-Psyshock always, you need to run pretty much a fully Physically defensive spread: 244 HP / 252 Def / 12 SpD Bold. If you want to get crazy you can run 172 HP / 252 Def / 80 SpD Bold which gets 2HKOed at the same rate at which a crit happens.
OK
For Blissey, keep in mind that 252 HP / 252 Def / 4 Calm has almost the same bulk as 4 HP / 252 Def / 252 SpD Bold, so the fomer is better if you are Wishing.
No Blissey can take a specs-Psyshock well, at best fully defensive Blissey can stall it out, but only if it has leftovers recovery (no sand). However it does take life orb-psyshock OK if you don't factor in stealth rocks. Anything less defensive is pretty much obliterated by boosted Latios.
For the 2 sets you have for Blissey, the only difference I can tell is that the Calm one is always 2HKOed by Life Ord-Psyshock Alakazam, while Bold has about a 50/50 chance to take it, not factoring in anything else though. The difference in bulk here is about 5%. Unless you are particularly worried about Alakazam, run Calm.
Sorry this is a bit of a mess, there really isn't a cut and dry binary answer, overall though:
-For Chansey, it is suggested you run a bit more Physical bulk than just 4 HP / 252 Def / 252 Calm. Your Bold spread does work, but it is not optimal if you want anything more defensive.
-For Blissey, you are probably better off running Calm unless you are worried about Alakazam.
I hope this helped you, sorry its a bit later here, so forgive me if this is a bit off.