Usually HTTPS will require additional effort both on client and server to establish the connection, and to do encryption / decryption of transmited/recieved data.
Moreover , HTTPS is not cachable, so resources and page will be requested over again on each page or each request. So it will be slower.
It worked fine on my wp 4.1.1 only problem (i could detect so far) is with google map that i used on some of my pages, it gives error “API had to be access over SSL” or something, so i have to use https on each page where i use google api to fix this. May be settings from google a/c can fix this?? haven’t tried that yet.
Sena