7.1 polk setup , need help

[Boogieman]

I just recently purchased a Hk 254 7.1 reciever and love it. I have all polk speakers in my current 5.1 setup, front- tsi 300 , backs - tsi 100 and cs 10 center channel. My question is should i purchase another set of the tsi 300's or tsi 100 for the other speakers to make it a 7.1 . I was wondering if the tsi 300 would be overkill since there just going to be for surrounds or will the 100's be better to go with.