The TR600 is a good cutter, but I find my TX900N eats the toughest or porcelain whereas my TR400 (they don't make them anymore) struggles. The TX has nearly twice the breaking power.
Some stats from the Rubi site......
TR-600-S 60 cm 42x42 cm 6-15 mm 600 kg 10.0 kg 13.0 kg
TX-900-N. 93 cm 65x65 cm 6-20 mm 1000 kg 18.0 kg 24.0 kg
Just got a Rubi TR600s with my CTD points, been using it a week and found it fine and light weight and very good for the money. You wouldn't go far wrong with one of those.
I have the TR 600 + 700 always on the van, i find they are fine and the right size for most jobs (including 600 x 600 porcs) I do also have the TX 900 and it's a lovely cutter but i hardly ever use it. Not a lover of Sigma myself, just can't get used to them.
I have five Rubi's got a ts60 its never been out of its case always used my tr60 but getting a bit worn so decided on the sigma have now got two and wished I had got them sooner nice cutters.