The spool of either turbo you are choosing doesn't matter when it comes to a 1/4 mile run. The rpms never drop below 4200rpm as long as you are shifting properly. Usable power is what is more key, and the ct20 has a lot more usable power in a drag race scenario. Clipping the turbine on the stock ct26 will get you a broader powerband, but the power output will probably stay the same or even go down a little. 240rwhp on a stock ct26 is going to be impossible unless you get headwork, like cams and port and polish, or you will have to use nitrous. A dude on the mr2 board made 260rwhp on a stock ct26 (at about 18-19psi because that was all the turbo could produce), but he had a completely built motor, completely built head and lots of dyno tuning. On that same exact motor he made 320rwhp on the ct20b at about 21psi (which it held to the shift point in each gear).

Water/alc injection will do what the stock intercooler is not doing, and that is cooling the charge temps. The restriction of flow you speak of just adds slightly more lag to the turbos spool. It will not effect it's performace at higher rpm since it will be all hot air blowing through the intercooler pipes at that point. The only gain I felt with the greddy sidemount was about 100rpm sooner spool and it did help cool the charge temps enough to dyno decent numbers. I did dyno about 10 hp higher on the stock intercooler though, on a day that was not nearly as hot as the day I dynoed with the greddy.

If you really still want to do an aftermarket intercooler, and want to be cheap, you can get one of those ebay honda front mount intercoolers for $225 and mount that in the trunk. Another $100 on various pipes, and cut a hole in the trunk lid, or the honeycomb out of the rear center panel.

I wish you the best of luck on getting 240rwhp out of a ct26.