I think Ganoid is running a larger throttle body, though he is also running headers and a honed/polished air intake manifold, so his performance would be different than yours.

Since you are going to run a larger throttle body, youi are probaly also going to run an open element air inatke system. This all adds up to more air going into the engie, so you need a way to get more air out, main reason you are going with larger valves right, so it wont make much sence to keep the choking oem system on. If you don't want to go with a complete header, than you should atleast turn each exhaust manifold into its on system and do away with the oem x-over. This would require modifying the stock manifolds some, but it wouldn't be too hard. So far after 2 yrs I am pleased w/my Downy headers, though I would recommend going with studs over bolts, the bolts seem to always come loose.