there's quite a big difference in the two markers -
Try the reviews available on pgi online or try: http://www.angel-owners.com There seems to be a wealth of info available there.
I just got a speed - any questions I've had have been answered. Including design/operating differences.
The speed has the lower pressure internals that allow more fragile paint to be used, also the IR3 has sh*te loads of bell's and whistles to play with/go wrong?
once it was calabrated my speed never chopped ever ,they are bloody quick as well, and as been said there lower pressure than the ir3.
ps i know where theres a nice black one for sale