Hello AB,
The datasheet recommends the TCM1-63AX+ balun from Mini Circuits for the widest bandwith solution that optimizes on performance. If this balun is not an option for you then whatever you decide to do such as driving the circuit single-ended or changing the impedance will result in much degraded performance. The linearity will suffer along with added power loss. It is very difficult to achieve optimized impedance matching at very wide frequencies like what you're trying to do.
The delimma you're going through with selecting a transformer is what had motivated me to work with Mini Circuits to develop this TCM1-63AX+. There is really no good solution out there that would allow you to achieve performance and bandwidth other than the TCM1-63AX+.
Qui