Carreraplanes,
My experience, and the related experience of a couple of excellent race mechanics, is actually the opposite: even the "S" pumps result in a lean condition at high RPM under load.
You are correct to focus on attaining the proper mixture, however. As has been written here extensively, most recently by famous race driver, shop owner and all-round great guy Grady Clay, as the MFI system ages the tendency is to go very rich.
My recommendation to you is to get all the systems in perfect order and then set the mixture. This would entail a thorough run-through of "Check Measure Adjust" to verify that everything is up to snuff.
In particular, you will want to remove and clean the thermostat and verify that you have, in fact, 25 pairs of discs in the correct orientation. WHEN THE THERMOSTAT HEATS UP THE ROD PUSHES OUT (sorry for shouting but I wanted to remind myself because I once got that wrong) so if you remove the thermostat you will actually put the rack into the full rich position. Your mixture settings MUST be made with the engine at operating temperature with the thermostat in the "lean" position which means that the paper tubes must be intact from the heat exchanger.
http://forums.pelicanparts.com/showthread.php?threadid=169445
Finally, I recommend the use of an LM-1 data logger for setting the mixture under all conditions. Using this relatively inexpensive device will allow you to precisely tune and verify the mixture under load, at idle, just driving around, etc. You don't have to install sensor bungs if you have a single-out exhaust, the Innovate people (Klatinn, the inventor, posts here) have designed a tailpipe clamp for temporary installation.
http://forums.pelicanparts.com/showthread.php?threadid=193331&highlight=inlets
With this device you should be able to set the mixture as lean as possible for smooth running and good transition. I remember it by 5-6-7-8, i.e. 5-6% CO at idle, 7-8% at 3000 RPM, but those numbers are very rich, you may be able to do better.
See also here for more excellent information:
http://forums.pelicanparts.com/showthread.php?threadid=269190&highlight=ultimate+mfi
Good luck!