I think most people end up around 15psi on a stock CT-26.
A better intercooler with lower pressure drop will make a big difference too. Not only does it cool better, but the turbo isn't pumping 18psi of hot air (out of it's efficiency range) to just get 14psi to the intake manifold due to a 4psi restriction at the stock IC. Even if the IC doesn't have better thermal characteristics you will end up with a cooler charge as the turbo isn't working so hard.
You should always get a baseline dyno performed whenever you install a significant mod like this. Just a baseline: A single pass on the dyno with the boost set to the desired level. Make sure the car is warm. Shouldn't cost more than $20... no tuning or multiple runs are usually needed. You're not looking for the best power, you're looking for danger signs in the AFR readings. If the shop isn't able to print out the AFR graph on the HP and TQ graph you need to find someone who can. I haven't ever had a shop tell me they couldn't, if you do find one it's probably amateur hour. They should also be able to tell you your AFR at idle while the car's on the rack.
Now let's get back to complicating things:
Here's where I am on the fence about the Lex AFM upgrade... Many people have said that some tweaking of the air bypass screw (sometimes requiring a longer screw) is needed to get the engine to run well at idle and low-mid load when in Open Loop. This requires a wide-band sensor to monitor AFR while making adjustments. Also, as there's always more performance to be had from a nice clean tune a fuel controller can open things up quite a bit even with the Lex... So, why bother with the Lex AFM? Perhaps just go with the 550s, stock AFM and a fuel controller? The stock AFM is a bit more of a bottleneck, but you'll never move enough air through the CT-26 to see it. With a fuel controller you don't need the Lex AFM, you just need more fuel per cycle. So, in exchange for a little more of an initial investment you gain more flexibility and a bit more performance... Older model fuel controllers are very affordable these days.
So you like the idea of a more tunable system but still want the reduced bottleneck? Well, you can run the Lex AFM and a fuel controller, but it may be worth considering a system such as the MAFT Gen II which will allow you to run a GM MAF (the 3.5" is HUGE) and has a built in fuel controller. It's also capable of spark advance control, datalogging and can be integrated with a wideband controller giving you a nice mobile tuning platform (laptop not included
).
I'm assuming you have little or no experience with tuning though and the setups I've discussed grow steadily in their learning curve and complexity. I'm just trying to set out the common choices and the ins and outs of each in a brief fashion. The Lex is still the easiest and cheapest if you find you don't need additional tuning to get it running smoothly with your setup. If this is your daily driver I'd stick with the Lex for now, you can always sell it off later if you decide to move on to another system and you'll still want the 550s.