flew my bit longer mini fat boy and sprint xl Saturday launched the mfb twice, once on a B4 - 4 & once on the 'big' motor a C6 - 5. the B4-4 was a rather tame flight to about 300'(good demo, small field motor), the C6-5 got it up and moving quickly guesstimate 750' the original 12" chute worked well and had no problem handling the additional weight.
the 'Astron Sprint XL' was flown on an AT D15-7t, deployment was a trifle late perhaps but should be fine in a low wind condition. I used a 15" thin mill chute that was just right. my suggestion is to resist using a 'big' motor for the 1st flight a D12/D15 puts it up around 800 - 1000' quite readily.
rex