Advice on Monthly P+I Payments (or Should I Go Back to I.O.)?

I just wanted to put this to the good folk on here.I've always held my two investment properties loans as variable interest only. About ten months ago I changed them both to variable P+I (paid weekly) with the interest coming out of the redraw on each property. It appears though that I'm hardly getting anywhere in reducing the debt? I've been paying an extra $1k-$2k extra a month on my repayments to try and cut down the debt. 
My question though comes from what a property investing friend told me. He informed me that for the first 7 seven years (roughly) you are only really just paying interest before any principle reduction begins to kick in. Therefore, he told me that I am better off going back to holding both properties as IO again and to continue paying any extra 'myself' on top to reduce the balance? Does this sound like a quicker way to reduce the balance or should I just be patient? My main goal is 'debt reduction' on these two investment properties. I watch how the balance goes down each week (plus what I add on top) then that once a month interest fee on each just seems to gobble up my extra repayments? Many thanks in advance!
Cheers,
Gats!