2 degree advance i can see you gaining that much but i wouldn't recommend it. i know from mapping hte 3sgte engines i specalise in you normally see around 10bhp estimate for ever 1 degree of ignition advance you run so 2 degree's on a small engine seems plausable.
Also another thing is what about 2 degree's retardation on the exhaust cam? retarding the exhaust cam would mean the cylinder pressures are kept in the cylinder longer creating more power but little bit more lag. advancing exhaust cam opening will lower power slightly but increase EGT's and turbo responce and spool.
again on the 3sgte you can gain around 10rwhp on a stock engine by retarding the exhaust cam 4 degree's
not sure how you'd do that on your single pulley engines though.
Guess you could retard both cams which would push the power band upwards to the right on the dyno, possibly giving a little more top end power gain but you'd have to run this on a dyno to test it out.
Tim