Not to start anything without DFASTEST not chiming in first...but that K29(engine is built to take 24 psi...not sure what the turbo theoretically could max out at) he runs is usually at 1-1.1 bar day and night unless he is not sure of what the other guy is packing.

 

I know dfatsest951 is a chat room hero, he does have a nice car, but to put it simply you are wrong. Here is a reply he had too YOU, just to help clarify what boost he runs.

So it seems 18.85 psi is the highest he has run, and only on one time. So basicly he car has never made its Advertised power on the street. Which is a good thing because the 14.5psi he runs daily seems about right for that #8 hotside. I tend to run 16-17psi on the street on 93oct, and on the track I run 21psi on 100oct. So if I am on the track for 1/2 and hour a session and WOT 70% of that time, it could be said that my car can really and properly run that boost with no issues like too high of back pressure. I have also run 21psi on the street with 100oct. This is no problem as my hot side is big enough.

Andial I think you should go with the #8 if not a #10

 

I am not an advocate of a 27/8 on 2.5 street car (I had one on my car in late 90's when Powerhaus was pushing them) as it is laggy, and frankly there are better alternatives such as Vitesse now. However that being said, you may want to check with Clark as in Clark's Garage. He had a 27/8 on his 2.5 that he HATED, due to the lag. He built a 2.8 using the same Andial components you have, combined with some head work, namely larger intake valves from an 89 2.7 NA. (I forget who did that in late 90's) but anyone can do it now.
In any case his 27/8 came alive with that combo. No lag issues, and he was satisfied with the performance.

Now all that being said, as others have already pointed out, to convert your 27/6 to a 27/8 you will need a #8 turbine as well as the #8 hotside.
These parts are not cheap from KKK, so you are likely looking at picking up a 26/8 just to get the turbine and housing and then send to a rebuilder to for a complete rebuild/balance. If you can find a 26/8 for 300.00, then you still need 500.00 for a rebuild. At that point, I would suggest you consider a turbo with more future potential for upgrades such as the Vitesse. If not, just live what you have until you need to rebuild or replace your existing turbo.

Good luck in what ever you decide.