Hi Darnun,
for the same (or better) viewing power (brightness), you will need the same (or larger) diameter scope. It's the diameter of the tube (ota) that determines the amount of light that can be gathered - or viewing power as you call it.
The Mak Cas will have a slightly longer focal length, (typically 1900mm or longer versus the 1200mm for your present scope) which means you'll be able to get a fair bit more magnigification out of it just by using the same eyepiece that you already have.
Hope this helps
