When you say "the way to go", what is making you question it?

space? i gotta have it in my room, so im limited to space and also i guess the amount of time i need to put into take care of it

What about your budget? There will be a bit of cost diffference in setup and maintenance between the 45g and the 70g.

What are the dimensions of the 45g?

45 is 25x25x16 i believe

Your current light would be pretty good over the 45g, so you wouldn't need to upgrade your lighting. If time, space, and/or money is of concern, I may suggest you go for the smaller tank.

my opinion is it comes down to funds. If I could have a 45gal that I had set up EXACTLY like I wanted, or a 70gal where I had to make some sacrafices, i'd do the 45gal... It'd probably work out better in the end and you'd get more enjoyment out of it. Just my opinion though....