I contacted them to get their opinion... They suggested their 55mm with the 5.3gps injectors. He also suggests that that set-up would net 5-7% increase in power. I would guess it's be closer to 10%.
So... With an engine like this, which is capable of a conservative 115hp/120tq (per their website), and my TB, it looks like I'll be over 100/100 still, which I'm pretty ok with for now... Problem is, I'll be running the snot outta my injectors. IS that really a problem?

 

HPi told me the same thing 5.3 injectors, after talking with art and there tuner at R&R cycles out of new Hampshire & dan thayer my tuner they recommended the 4.9 injectors said they would support 130 hp with out any issues. going too big on the injectors some time causes tunning issues I was told! your bike I believe came with the 4.2 injectors and that will support your build. like vdrop stated that kuryaykn 57mm is a great deal. but its only money they make it every day! the HPI is a Nice unit. my duty cycle was under 80% so there was no need to go to the 5.3's which I brought with me just in case I needed them.