Lionel Fastrack Interlocking

How big are your locos? Larger switches will always make a layout run smoother, regardless.

You could split the difference and go with o-48.

In my experience, its less likely the a loco will stall on the larger switches as well. 

What's the spacing on your loops, center rail to center rail?

Are you using 048 & 036 curves?

The switches are the same price in FasTrack. I agree with RickO. Go larger. You can always use them when you grow to a larger layout.

Yup. The larger switch setup would occupy a side, but you could put all four on one side.

Attached is the 072 switch setup from the FasTrack modular plans. Keeps a 6" spacing.

The 036's will probably be easier to fit.  

If this picture displays well, this is the easiest way using O36 switches. 

http://local.trainz.com/newsletters/jan10.html#Plans

Here are 2 plans I made up... If you have any suggestions or modifications i'm all ears.

I prefer your second plan ( on the bottom). It allows for more interesting operation possibilities. I.e. you can park one train on the ouside loop and pass another  one to the inside or vice-versa. It also gives you more options for dropping cars and getting them into the sidings.

Having the switches seperated minimizes and issues with power interruption  of multiple switch gaps. 

Thanks for the heads up Rick... The bottom used o60 turnouts. I will use o36 in the middle for switching operations