I have a clever little spreadsheet that I copied from someone who actually knows what they are doing . Based on the thermal resistance from the junction to the case and from the case to a heatsink and calculating the RDS at a realistic 40 deg. C ambient temperature, the sheet shows the current handling without a heatsink and the thermal resistance of the heatsink needed at various current ratings. I have modelled several other common FETs in the sheet and it has proven to be quite accurate. I had to guess the thermal resistance from the junction to air, so the power handling could be higher.

I am not dissing that IXYS fet - it has some great specifications but it's still not a magic bullet for a HW controller and you will still need a bucket of them. Its a pity that they don't state the current handling of the pins; with a custom package like that its hard to tell. Keep in mind that this is a HUGE surface mount part at 32 x 25mm so an array of them will take up plenty of space, which is why I still prefer the TO247 case FETs.