The efficiency difference between say 8:1 and 9:1 is about 3% so you're not really going to gain any 'off-boost driveability' - that's just an old wives tale.

All I will say is if you haven't purchased the parts yet (as it's blatently an internet spec - off the shelf crap from America, where they mainly run superchargers and low boost levels), is have a bit of a think about it. They have drawings over there with JE, CP, Arias etc. for proper low-comp pistons and can sell you those.. From experience, anything over 8:1 isn't going to make a genuine 300bhp on pump fuel - you WILL get unavoidable det before that point and it doesn't matter how much you think you can drown the engine in fuel, it'll still be there!

I'm just trying to save you a lot of money and heartache..