Last July I purchased an Anthem MRX520 receiver and Paradigm 75F's, Center 1v7, Surround 1v7, and a Sub 8. My room is 1400 cubic feet. I had auditioned a pair of 95F's prior to purchase and loved them. Their bass response was awesome. After a little thought, I realized that the 95's would be too large in such a small room, so I opted for the 75's. I ran ARC several times (before and after speaker break-in) and I'm very happy with my purchase.
I believe going with towers would be a better choice than upgrading the subs. After looking up the SVS SB-2000 subs, I find it hard to believe that you would need more low end bass than you already have. The towers would be the way to go. And, for a room the size of yours, if you can spring for the 95F's, I think you'd be blown away.