I tried to find out but it seems that the mSATA specification is not freely available (paywall) and other sources on Google’s search results didn’t help.
I would suspect the standard power ratings to be the same for mSATA and miniPCIe. In the case of miniPCIe the maximum normal power for 3.3V is 3.63W and the maximum peak power for 3.3V is 9W (100-microsecond period).
BTW WLE200N2 is rated 1.9W(Max) and WLE900VX is rated 4.7 W(Max). In the worst case their power consumption together is 6.6W and half of it is 3.3W so the lower rating of WLE200N2 might help balance the higher max power rating of WLE900VX. I don’t know typical values for the cards.
Every chain doubles the output power. So 20 dbm * 3 chains gives 26dbm. Add the antenna gain of 5 dbi and you get 31 dBm EIRP. Take away up to 1 db signal loss in the cable, connectors and diplexers and you are at 30dbm EIRP. This is the regulatory limit for 5 GHz in germany if you have working TPC.