Hey Sredze,
As others mentioned, the Power Primer (http://www.mrcontrols.com/primers/power.htm) is an awesome reference.
 
I also was given this book (http://books.google.com.au/books/about/Toyota_MR2_Performance_Hp1553.html?id=3k-MwlZpT20C&redir_esc=y)
when I bought mine this year, it talks of staged builds (1-3), covering the whole car including engine. In it "stage 2" stops short of turbo upgrade (except maybe for a CT27 or CT20B), giving you around 200rwkw.
If the book had a "stage 4" it would just be a pic of MR2QIK's car

def the CT26 running out of puff after 6000rpm gets tiring after a while...my next plans are first to get rid of the nugget and bolt on a 'CT20B', some sort of CAMS maybe (N/A ones), do a full seal kit inc. HG on the engine, as it's leaking oil from likely the cam and crank seals. then implement a MAP ECU and AFR and IGN tune it properly... which should keep me happy for a  while. :)

This is the way I got my 250rwkw (probably good for ~280rwkw with better cooling):
 
Staring with a gen3 motor:
 
Rebuilt motor with CP pistons and Eagle Rods 
1mm Oversize Ferrea valves 
Garrett GT3076R twin scroll turbo @ 21psi 
HKS 264 cams on HKS valve springs 
Greddy Pro Spec B II EBC 
Apex'i Power FC & Commander Tuned by HITMAN 
Berk Technologies Dump pipe 
Hi-Tech Mufflers' 3" Exhaust 
Apex'i Air Pod 
Border top mount intercooler
800cc SARD injectors
Walbro GSS341 fuel pump
 
 
If I could do it again, i'd swap the GT3076R with a GTX3071 (still might do this). I'd hit the same power ~250rwkw but it would come on boost earlier and generally have more area under the power curve.
 

im not sure that you need to play with valve sizes to achieve 300kw.
 
longer duration cams with standard lift should do the trick and allow you to run higher boost without problems associated with inlet pressures opening valves. going up in valve size increases the pressure on the valve springs and means they'll degrade faster and start lifting off the cams as high rpm. 
 
i guess you could choose.
do the valves and run lower pressure.... or a turbo that spools quicker but doesn't hold peak pressure at high rpm so is effectively lower.
or,
run a turbo that can produce 20psi at high rpm and increase the opening duration but not the valve size.
 
the stock gen 2 head and cams are good for 200+ kw @ 14psi and about 6500rpm

Personally, unless going hardcore (ie 400rwkw+), I don't see the need for oversized valves. Given there's been quite a few documented issues with Ferrea valves I don't see the need to take the risk for a marginal improvement. There are examples of standard valves on 800hp applications (eg MR2Liter in the States).

my first advice..
do not overcapitalise on the car.
 
2. GT35R is very fun at 1.7 Bar
 

I'm pretty sure the ferrea valve issue is only with their cheaper ones.

You're right you don't need the valves. I ended up doing it because my original valves were bent, so i changed them anyway.

hey! to be fair.. 
i only had the valve issue because of a **** set of the ferrea6000s that had a problem
ferrea replaced them for free but i upgraded to the Competition PLus valves for an extra 60 dollars.
 
then i never had a problem.
 

To be fair.....it is likely only an isolated case(s). But it's another aftermarket item that can fail when Toyota valves are proven. One thing I've learned over the years, is to avoid changing items just for the sake of it (but we all do to some extent).
 
2. Richard can't say he never had a problem afterwards because the car was sold shortly after it was repaired. Many of the big HP US 3SGTE's have had valve issues for numerous reasons.