get yuourself over here mate,
http://bbs.rsownersclub.co.uk/forumdisplay.php?f=134
and check out the for sale section loads of very well looked after examples,
its a very busy forum with lots of people eager to help out, and a vast range of knowledge and solutions to problems,

300bhp is very easy to acheive for very little work,
and more if you fancy it, some cars there are running close to 390bhp on standard internals, just a hybrid turbo and fueling upgrade, and those with fully forged engine build crossing the 400bhp barrier and beyond,

can fully recommend owning one they are fantastic cars, handle well, very reliable, all the usual problems are simple to diagnose and fix, and a wealth of products available and more being developed all the time, you really can set up the RS to exactly how you want it,

and as for standard power versus and astra GSI,
I know that a std Focus RS walked all over my freinds MK4 2.0 coupe turbo (think they have the same engines as the GSI), and handling wise they are far better with the sachs dampers and brembo brakes as standard, you wont regret coming over to the RS mate,