Extra Diffclk inputs with Cyclone IV

I'm trying to connect 9 differential clocks to a Cyclone IV (EP4CGX30F484). These are from 6 analogue to digital converters that are not necessarily synchronised and 3 other clock sources. The 6 ADC clocks and one other will go up to 80 MHz. The other two will be at 100 MHz and 250 MHz. These will all come in as LVDS signals.

The number of available global clock networks (GCLKs) is 30 for the device, so this is not a problem. My worry is that there are only 6 pairs of differential clock inputs listed in the Cyclone IV user guide (but 8 listed in the device's pinout document(?)). I know you can connect to GCLKs with internal logic, so I should be able to use standard differential I/Os if needed.

My question is what are the implications of using these standard I/Os instead of the DIFFCLK inputs? Will there be delays and should I be concerned about the frequencies I'm using?