There is a couple reasons for the HTEV...one is to improve low end power...below 3-3500 rpms...I dont know about you all but i almost NEVER ride with the r's that low. The second is to help modulate fuel economy and emissions(in conjunction with stock FI mapping)
I just installed my eliminator from Haas Motorsports and will be getting the bike out for a scoot this weekend and let you all know the results. They were great to deal with, the price was EXCELLENT and the product is very well made. plus...they send a custom PC map with the kit.
I see no reason to think it would not be much off a full system. I had a collector/crossover box eliminator made for an 86 VF1000R a few years ago and the difference was pretty dramatic.