about 110" is the widest i like to tackle with my long-arm, and yes, theoretically you can co up to about 120", my table is 14 feet long but not all of that space is available for quilting space, there is space on each end of the bars where the machine rests and you need some 'work-space' in order to do larger than that 110"; prep work has to be done and i would probably have to load, do 1/2 unload, move over and reload to do other half, it would cost alot extra to have it quilted. so i would recommend trying to modify your design to accomadate. if you have a long-arm quilter you usually go to check with that person and see what the limitations and recommendations are for his/her set up.
and although it was stated that lenghth does not matter that is not necessarily true...the longer it is the larger it is going to roll up to be that "roll" will take up throat space on the machine so you may have had 12-18" of quilting space in the beginning of the quilt and find there is only 4" of quilting space nearing the end because the rolled quilt is taking up the space...it is best to check with your quilter.