How high can my credit score climb if I have only credit cards in my credit history?

My current credit score is 745 and I’ve built it solely by using credit cards and paying on time (but never had any loans). Somebody told me that the abscence of installement-paid loan will prevent my score from climbing much higher. Is it true? Should I take some consumer loan to boost my credit score [...] http://bit.ly/ogruzd