Need advice on new front speakers for Onkyo receiver

[cagenuts]

Hi there

I currently own an Onkyo TX-SR600E receiver with the following speakers;

Polk RT5 Bookshelves acting as front speakers (8 ohms, 20 - 125 w/channel, Efficiency 89 dB)
Polk CSi30 Center
Polk PSW350 Sub

The receiver has these specs for output;
Power Output* (8 ohm, 20 Hz-20 kHz, FTC) -
Front L/R 80 W/Ch
Center 80 W
Surround L/R 80 W/Ch
Surround Back 80 W
Power Output* (6 ohm, 1 kHz, FTC) -
Front L/R 105 W/Ch
Center 105 W
Surround L/R 105 W/Ch
Surround Back 105 W
Dynamic Power** (front) -
3 ohm 215 W/Ch
4 ohm 160 W/Ch
8 ohm 95 W/Ch

The sounds is a bit low so I was thinking of sending the RT5s to the surround back l/r and then getting new front speakers.

The question is how do I size the speakers? What size, power etc?

Any input is appreciated.

Thanks.