700tvl is a myth anyways.
A good quality balun will have no visible impact on the signal.
Our analog cameras are about evenly split between coax and UTP, with most of that passive-passive using baluns. Although there are slight differences in signal levels between the two cable types, we have yet to see any advantage in video quality of one over the other. We did not actually quantify the signal differences since we couldn't see any difference.
Years ago, we tested a number of baluns from various manufacturers and determined there was literally no difference in video quality between balun manufacturers. In this case, we did test the signal using an oscilloscope and an FM Systems Camera Master and measurements showed no more than 1db difference between baluns. This despite the claims of NVT and Nitek that their products are superior. I guess they are if you only equate quality with price ;-|