I started off with copper insulated cable, then stepped up to gold when I needed it, and finally had to use the 1-diamond-per-block glass fibre cable when I got to 8192 EU/t. As Omicron pointed out, the IC2 Exp requires glass fibre for the highest throughput.
And, while 1 diamond per block is expensive, it's not that expensive by the time you *need* it. When my starter, slow machines were only 32 EU/t max., 1 diamond was expensive. But, by the time I had 3 or 4 transformer upgrades in 9 or 10 machines, 1 diamond per block for a total of maybe 15 to 20 blocks wasn't that expensive.
And, I learned the hard way about the new 'voltage'. When a machine or a power cable has a maximum rated voltage, that's the maximum of all suppliers summed up., ex 2048 EU/t + 2048 EU/t = 4094 EU/t, which will blow any cable below a fibre cable and will blow an MFSU.
On the bright side, you don't need an HV transformer in reverse mode to get 8192 EU/t. My power setup now for my processing machines is a bank of RTGs and Geothermals - all relatively low voltage output - feeding into four(4) MFSUs in parallel. Those MFSUs - in parallel - are driving a single glass fibre cable feeding into my machines, which all have transformer upgrades to handle 8192 EU/t.
Before that, I was using nuclear, but it's too much work for too little power. Fiendish Bees producing lava into Geothermals is maintenance-free. I also haven't setup UUM, but I find UUM to be terribly anti-climactic, so I doubt I'll bother unless there was an actual need for it.