On my old Selco thermostat, I have the following wires:

W2 - White
O - Orange
X - Blue
R - Red
G - Green
Y - Yellow

My new thermostat has the following terminals:

G
RC (jumper to RH)
RH (jumper to RC)
Y/O
W/B
Y1

I believe that R (Red) will connect to RH, G (Green) will connect to G, Y (Yellow) will connect to Y/O, X (Blue) is common and not needed. I'm not sure about the Orange and White wires though. Can anyone help me out with this one please?

Model numbers and brand names for both thermostats?