Yes, you are at the right place.
You didn’t specify, but I suppose you are an inch guy (as opposed to mm or cm):
The pixel file size:
36x60@200ppi should result into 36x200 pixels in one direction (7,200 px) and 60x200 pixels into the other direction (12,000 px). Anything else is not correct! So your CS5 numbers are not correct. I would say your CS5 numbers are cm (1inch = 2.54 cm).
Colour mode possibilities:
Then there is the bit depth: you may have bitmapped (black and white, one bit per pixel), you may have indexed (8 bits per pixel, and a table of up to 256 entries, giving 256 distinct colours) or greyscale (usually 8 bits per pixel) or “true colour” 24 bits per pixel (8 bits per colour channel) or 16-bits per colour channel or even 32-bits per colour channel. You will understand that if you put more bits depth in the image, that the image size will grow (1byte is 8 bits). For print you will need CMYK instead of RGB, adding one colour chanel, adding more storage space need. But to make things again more complex, there are also other colour models that have their use. But let’s say that there are for the standard (starting) user 2 colour modes of use: 3x8bits and 3x16bits RGB.
Your indication:
This said, you did not say what 3 options you had for saving. And you did not say what you did to “make your file 50%”.
What I can imagine is that you made your file X bits depth and there not all the save options are available, because not all the file formats support all the bit depth.
However, in the real world of today, there are only 4 file formats of use (the other have their purpose, but you need to know what you want to do).
JPEG
PNG
TIFF
PSD
Of those 4, the PSD file format is the natif one for Photoshop. TIFF and PSD can save all the features that can be saved with Photoshop. PNG saves a flattened picture at max 3x8 bits, that may contain a transparency mask. And finally JPEG saves a highly compressed picture, but only 3x8bits and no transparency. In addition, the compression is destructive, meaning that with each generation you will loose quality.