Use the verticals, I'd say the power/weight ratio is close to a 109G2. Max speed is not so good, you can use speed to reduce the number of people in the fight but don't expect to outrun most mid war planes. Good wing area so the flat turns are good, but don't get too cocky at low speeds or you might experience a hardly recoverable flat spin.
Never take the additional 20mm's, the pay to price on weight and aerodynamics is too big. Firing the 20mm's only at longer ranges is a good way to make faster planes to turn, as they don't know if you are firing the 30mm's or not and will not risk to keep giving their 6.
Don't take more than 50% internal fuel unless you are going very high (not a good option IMO as the 110G2 performs not very well up there). Above that 50% the flatspin problem will get much worst.